Was it something like some guy just said "Hey, the word "the" in my new language is "el" and "hello" is "hola" or something along those lines, because that seems like it would be very complicated
Morphemes are individual units that mean something. For example, the word archaeology has two morphemes: archae, meaning ancient, and ology, meaning the study of. Speaks (as in he speaks) has two morphemes as well. Speak, meaning to talk, and s, meaning third person. Languages has language and s.
There are three main types of languages: isolating languages like Chinese, where there's only one morpheme per word, agglutinative languages like Turkish, where words are strings of morphemes, and fusional languages like Latin, where different meanings are combined into single morphemes.
Languages go through something called the grammaticalization cycle. Basically, the different words of isolating languages combine into strings of morphemes as the language evolves, and the language becomes agglutinative. The morphemes in agglutinative languages combine into single morphemes, and the language becomes fusional. The fusional morphemes gradually disappear, and the language becomes isolating again. Every language is continuously going through this cycle. For example, English is fairly isolating, but the word not has turned into the morpheme -n't, which attaches to verbs. This is an example of English becoming more agglutinative.
Onto the other part of your question.
Linguists have no clue whether all languages (except Nicaraguan Sign Language) have a common ancestor. It's simply too far in the past to determine whether Proto-Human language existed or whether different language families appeared at different times.
Almost all European languages (with a few exceptions like Basque and Hungarian) evolves from Proto-Indo-European, which was spoken in about 3500 BC. There are no records of this language, but linguists have mostly reconstructed it by comparing its descendants, such as Sanskrit, Ancient Greek, and Hittite. Proto-Indo-European grammaticalized into a number of other languages, one of which was Latin. Latin then grammaticalized more and became the modern Romance Languages. I don't know much about the history of Spanish, but hola came from some word in Latin, which came from some word in Proto-Indo-European, which came from some word in an earlier language that we don't know of. Hey came from the Old English word for hey, which is from the Proto-Germanic word for something, and the came from the Old English word for that. El also came from the Latin word for that.
Sorry for the wall of text; this is a subject I'm very interested in.