The 1920s film industry (in the US, since I’ll assume you’re referring to Hollywood) is usually considered the unofficial start of the ‘Golden Age’ of Hollywood cinema, where studios were divided into majors and minors which dominated the industry’s output, each studio had a certain house style which distinguished them, and actors had exclusive contracts with studios, often limiting the kinds of roles and movies they would make. In many ways this is much different than the modern US film industry, but in other ways the way the industry worked wasn’t wildly different than today.

Talent agents existed, and studios were constantly scouting for new talent. A studio like MGM (which is emblematic of the studio system as a whole in most ways) would look at extras, models, dancers, and stage/vaudeville performers to find someone who fit their style and could be turned into a bankable star. Because contracts were exclusive (and during the silent era, almost no one fought against limiting contracts except for the founders of United Artists), finding a Joan Crawford or a Greta Garbo could guarantee years of successful films based solely on their names. Because silent movies were, you know, silent, a proper speaking voice, elocution, and accents weren’t impediments to careers, and a limited range could also suffice for silent actors. This isn’t to say there weren’t many talented actors working then—simply that studios could take an actor, say an 'exotic beauty' type like Pola Negri, and continually make movies where she played essentially the same character in essentially the same settings, with little variation. While there are actors that have this same appeal today, it’s much rarer, as a large range and ability to work in all kinds of genres is valued today (and has been for decades.) Today, studios also lack the ability to fully mold and control a performer’s career the same way they could in the 1920s and up through the 1950s. As for talent agents, there were people like Myron Selznick, the brother of producer David O. Selznick (who in the silent era was just working his way up through the ranks at MGM), who began working as a talent agent during the late 1920s, though usually agents would assist studios rather than forming their own agencies.

Studios were also structured and run much differently. During the 1920s, the major players—MGM, Famous Players/Paramount, Fox, with Warner Bros. and Universal being less prestigious and United Artists basically the equivalent of indies today—produced far more movies than studios today do. MGM would divide their product into categories, with ‘A’ pictures having large budgets and big names. These would be your The Big Parade, your Ben-Hur. Then there would be programmers and ‘B’ pictures, usually much shorter, cheaper, and with less well-known actors. Westerns were particularly known for being programmers, and Western actors would usually churn out cheap, short movies several times a year, with little variance. Block booking, the practice of tying weaker films to one big surefire blockbuster hit and forcing theaters to accept the whole bundle, was also rampant in the 1920s. Studios also controlled theaters, and one reason MGM became so successful was that it controlled major theater chains in prime locations like New York. Today, while studios like Disney increasingly control more and more share of the market and even theaters, they still produce less films and don’t rigidly structure their films along ‘A’ movie, ‘B’ movie lines.

The 1920s was also the period when film and fan culture as we know it really began forming. Fan magazines like Photoplay (founded in 1911) and Screenland (founded in 1920) hyped newcomers, obsessively detailed the lives of stars, and sadly chronicled the decline of fading stars. They shared many of the features of modern tabloids and magazines, including film reviews, both ‘serious’ and ‘fluff’ interviews with actors, high-quality photos of actors, contests voting on best actor/best dressed/etc., and gossipy articles about actors’ personal lives and personal dramas. Before the Academy Awards were created (first handing out prizes in 1927), Photoplay would award their own prizes for best picture, selecting blockbusters like The Big Parade in 1925 and Seventh Heaven in 1927. Because studios would sink so much time and money in their ‘A’ pictures, they would heavily promote them before release, especially if an actor’s career was tied to it. A movie like The Four Horsemen of the Apocalypse from 1921 could be compared to a movie like the upcoming Dune adaptation: based on a popular book, starring two young actors who are still relative newcomers (Rudolph Valentino/Timothee Chalamet and Alice Terry/Zendaya), directed by a well-regarded director (Rex Ingram/Denis Villeneuve), and Horsemen even had a well-known screenwriter attached (June Mathis, who basically handpicked Valentino for the role.) In both cases, audiences were primed for the film months in advance, with publicity photos, interviews, and the like being released to build expectations. While Dune hasn’t been released yet, it worked for Horsemen: it was a massive critical and commercial success (box office data for the silent era is sketchy, but I’ve seen claims it was one of the top ten or top five highest grosses for the 1920s) and built Valentino’s career.

I unfortunately don’t have my film history books with me right now, but a good place to start for more is The Genius of the System by Thomas Schatz, as it covers the entire studio system era; the first few chapters discuss the silent era. The Media History Digital Library also has a section where you can view fan magazines from this period, including Photoplay and Screenland, if you're interested in reading primary sources for this topic.