Instead of browsing via URL, companies could buy "AOL keywords". A user could just put in a keyword, like "dog food", and AOL would send them to a particular dog food page. In the days before good search engines, this was very convenient even though it was obviously pay-to-play.

https://www.youtube.com/watch?v=1npzZu83AfU

When dial up Internet was a thing, AOL was the leader in that universe. It was basically one of the earliest walled gardens out there. They had their own chat, email, etc. You accessed it all through their desktop client. You never had to leave the AOL application to experience "the internet". They of course were still providing general Internet access, so you could still fire up Netscape [and earlier browsers] and cruise to whatever websites you wanted. The Internet eventually eclipsed what AOL could offer for most people and their premium price and sometimes dodgy Internet service eventually fell by the wayside to a more open Internet experience for most users.

Edit: AIM was a really popular messaging client for years after the fall of AOL as a premiere dial up Internet service.

Movie trailers often had them, sometimes long after AOL had declined in relative popularity. An example I mentioned in another comment was at the end of one of the lord of the rings trailers:

https://youtu.be/V75dMMIW2B4?t=143

I have no idea how popular they ever were, but I'm sure there's a large segment of people that find it easier to remember and to type in "Lord of the Rings" into their computer than "www.lordoftherings.net".