It grew organically. For purposes of this discussion I'm going to divide the time period of the internet into the "early internet" pre-1994 and the "web era" after that.

In the "early internet" there was a diversity of protocols and tools for sharing information. Email would be familiar, and still exists of course, but there was much more. People would dial-up directly to "bulletin board systems" (or BBSes) to share files or chat in a forum format (similar to the way reddit works now, in fact). There was also usenet, which was similar to BBSes but used the internet directly. Usenet newsgroups were divided into different subjects (like sub-reddits, but heirarchical). People would use newsreader software to participate and universities typically ran the news servers themselves (usenet is a store and forward protocol, every local server basically has a cache of all the posts). FTP could be used for file sharing. And there were many various systems for sharing and organizing different kinds of information. One of the more popular in the late days of the early internet was gopher, which used a filesystem type organization for content but allowed mixing textual content that you could view in the client with other kinds of data but didn't have the flexibility that hypertext would later bring to the table.

There were also a lot of different services that would use a telnet based interface. To use your college's digitized card catalog you might telnet to a specific server and/or port and then navigate the textual interface presented to you. There were also social uses for such things such as MOOs, MUDs, and chatrooms. You would log into a server and be able to chat with other people or you'd be able to play an interactive text-based game with other people.

I should point out here that during the early internet period most of the users of the internet were college students and faculty, researchers, or government workers. This grew out of the early years of the internet's growth as a tool for collaboration and research. In the late days of the early internet it was a bit like the Holy Roman Empire, a patchwork of different big fiefdoms with the NSFNet (National Science Foundation Network), MILNET, and other big pieces all fitting together. It was funded primarily by government or academia and generally a non-profit endeavor.

So, to summarize. The early internet was primarily used by government and academia, was non-profit, and used a wide diversity of protocols, each with their own software client/server software for using. For example, for email you might use "pine", for usenet you might use "tin".

In the early 1990s people started looking at ways to better improve collaboration and sharing of structured data. It was actually surprisingly difficult to share data back then. You could package something up as an email attachment, but referencing a specific thing was kind of difficult. So people thought of ways to encapsulate references to specific things (resources) on the internet using some sort of standardized scheme. At the same time people were thinking about how to embed references to resources in material on the internet and how to improve the presentation and layout of information. It was pretty easy to view plain text material on the internet at the time, there were lots of different ways to do it (gopher, usenet, email, etc.) but it was clunky and cumbersome to share formatted documents. At the time there was still a diversity in WYSIWYG style print-ready document formats (MS Word & Publisher, LaTeX, wordstar, word perfect, etc.), and none of those formats was at all suited for sharing in a digital-only context.

Some folks at CERN, primarily Tim Berners-Lee, Europe's main particle physics institution which has run some of the most powerful particle colliders on Earth, came up with an idea for a new system for sharing information. It had a couple of interesting components and it heavily leveraged a lot of work that had come before, synthesizing it into something that was highly practical and functional. One part is the concept of a "URL" or Uniform Resource Locator. This was a way to systematize the complex diversity of information sources at the time. It's fairly simple, it breaks a resource location into three major parts: the protocol (e.g. http) then server address (e.g. www.reddit.com) and then the path to the resource (e.g. "/r/AskHistorians/comments/6t79tp") (plus some other stuff like credentials, ports, query data, etc.) One important thing to understand is that this wasn't just for http resources, this was for most anything that could be referenced, usenet posts, ftp files, email addresses, gopher links, telnet addresses, the whole nine yards.

Then there are the other two important bits of the web HTTP and HTML. HTTP or the Hyper-Text Transfer Protocol is just a very simple way to transfer data from a server to a client. It's actually shockingly simple, at least it started out that way. Like many other protocols at the time it's just a plain-text protocol. A client connects to a server (on port 80 by default) and then it sends a request, then the server responds by sending the data. It still works this way, or can. You can telnet to google.com at port 80 and type "GET /" then pressing enter twice, you'll get the contents for the google homepage in response. One important aspect of HTTP is that it's stateless. When you connect to a server via telnet or ssh you have a long-running session. The result of a command would depend on whatever context you were in at the time. HTTP is always fire and forget. Your client issues a request, the server sends the response (the contents of the "resource") and then the socket closes. Your client is instead responsible for keeping track of context (by saving resources in memory, using "cookies", etc.)

HTML is the markup language of the web (Hyper-Text Markup Language). It was based off of SGML (Standard Generalized Markup Language) which was developed in the 1980s as a general purpose way of marking up (adding structure and formatting to documents) textual data. HTML was simpler than SGML and added the concept of hyper-text linking via URLs. You could embed a link to another resource within an HTML document by referencing that other resource via URL. One of the key important aspects to HTML was that it was pretty simple, it was text-based (so you didn't necessarily need any special tools to edit it) and it could be written by hand.

URLs, HTTP, and HTML are the three components of the world-wide web, which got its start at CERN in the early '90s. Initially the browser software had only text-based UIs but even so there was a lot that the early web had going for it. It was easy to setup, easy to develop, and easy to use. You could build a website with a very modest amount of work, you could arrange, organize, and format your content how you liked it and anyone could access it, or reference it. Additionally, the simplicity of early web servers meant that it was easy to setup a server and get things running. And to navigate to someone's page all you had to do was know the address. The URL/HTML systems meant that it was easy to collect data into directories by just adding a link to a URL with some descriptive info to one page. The early web grew fairly rapidly due to the ease of creating content for it and the ease of use. But during the early internet period the web was still used almost exclusively by academia.

More and more people started putting content on the web and using it regularly to share research and information among one another. Being researchers, there was also a lot of development on the web. One of the major contributors of development in the early years of the web was the NCSA (the National Center for Supercomputing Applications at the UIUC). Students and staff at the NCSA ended up developing one of the most heavily used web server implementations at the time (httpd) as well as the Mosaic Browser. Mosaic was a web browser that used a GUI instead of a textual interface, it also had native support for many different protocols (like ftp and gopher) which is why it was named "mosaic". Mosaic, released in early 1993, put the web into the reach of non-academics.

At around the same time internet service providers (ISPs) began growing and offering more and more services to an increasing number of non-academic internet users. By 1993 there was starting to become a lot of things for non-academics to do on the web. As mentioned above usenet was similar to a forum system and was a popular way for many people to communicate with others on specific subjects of interest (which might range from discussing the TV show The Simpsons to talking about the details of interstellar travel). One of the problems usenet had consistently faced was that every Fall there would be an influx of new students into colleges who would then gain access to the internet and to usenet and begin participating without an understanding of the history or, especially, the etiquette of using the internet or usenet specifically. However, the Freshmen would typically learn to abide by the social norms of usenet and internet use in general fairly quickly since they were outnumbered and they had some stake in wanting to be accepted by their academic peers on the internet. In September 1993 AOL started offering usenet access in what came to be known as the "eternal September" due to the continual influx of new users who didn't care about abiding by the existing cultural norms of the groups they began participating in.

(part 1/2)

There were "bulletin board" services for about a decade before the World Wide Web went live. These services were essentially intranets, between subscribers and the company's servers used the Internet as its network, but didn't have the World Wide Web. The main services were Compuserve (the first, founded in 1979), Prodigy, GEnie, and America Online (all of which had launched before 1990).

In 1993, the two largest were Compuserve and Prodigy, and combined, they had 2.5 million subscribers, according to the Chicago Tribune.

By then, these services were targeting businesses, offering corporate accounts. These had reached home offices by then, too, helping them stay connected.

These "bulletin board services" ("BBS") were simply message boards, and a lot like Reddit, in that they were topic based and text based but since there was no World Wide Web, there weren't any graphics, really, unless the service itself (which was just an app installed on your computer) had them built in. And because these were apps, essentially, you couldn't view one service's bulletin boards if you were subscribed to a different service.

Over time, Prodigy, Compuserve, AOL, and GEnie started offering other capabilities with their services. They had all offered email pretty much from the start (and they charged by the email), but they also added games, shopping, chat rooms, and more.

These services began to be offered at some colleges and universities in the early 1990s, included with tuition, though many universities had developed their own internet services.

In 1991, the world wide web had been launched, but it wasn't until late 1993 that HTML had been standardized. Around that time, these bulletin board services began to offer web access at an hourly rate. The use of the internet began to balloon and one estimate had it that there were already 40 million internet users by the end of 1995 (though another estimate put at 20 million). Most users would still have been using one of the major services, Prodigy, Compuserve, or AOL. (GEnie kind of fell off.)

At the end of 1996, AOL stopped charging an hourly rate and instead charged a monthly rate for internet access and the world wide web exploded. AOL had been just one of the pack at that point but by the end of 1997 they had 11 million subscribers. That number grew afterward, but then we're butting up to the twenty-year rule.

EDIT:

And just to add a little bit more information, both Compuserve and Prodigy started out as "videotex" services. Essentially, they were like a teeny tiny centralized Reddit. You would launch your app on your computer through the command line, you would then type something or click a button which would connect your computer to the service via your telephone line-based modem. Once connected, at the other end, there would be a single server (or, later, a set of servers) that stored all the content of the bulletin board.

Over time, as these services built out their networks, they connected them to the wider internet of government, university, and corporate computers, and they became decentralized. However, as long as these services were in business, you did access the internet through their apps. It was after 1997 that any of them became true ISPs.

EDIT 2:

And just to address the questions in your body, the internet's use pre-1990 was mostly by university computer science departments (which, in turn, made it available to the wider university), hobbyists, or corporate users in particular industries (airlines, banking, etc.). So people learned about the internet because they were already interested in computers and went to school for it and/or worked in the industry, or else they worked in another industry that was an early adopter of the technology.

As more and more corporations began to understand the advantages of email over fax machines, they began to make the switch, and the use and knowledge of the internet widened.

With the launch of the bulletin board services, its reach among hobbyists widened, too, to the point that they had a few million subscribers by the early 1990s, as mentioned before. The world wide web, HTML, the Apple Macintosh line of computers, and the GUI-based Windows 3.1 operating system, all came together in the late 1980s and early 1990s to make computers and the internet more usable to the average person.

There almost certainly were some awkward user manuals in corporate offices for the uninitiated, though lots of people were introduced to the internet or BBS services by being sat down and shown by someone else. So you would get newspaper articles like this one quite often back then, where not only would the article announce the latest release of consumer computer technology, but they would describe what it was used for and why it might be beneficial to you or your business.

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