I think I will understand only what Jerboa makes easy to understand. I mean: there's a search function so I look for things there. There's a gaming community, so I suscribe. The frontpage or whatever show me posts from servers (?) I'm not subscribed to, so I will lurk there (like in this instance).
I don't know if I there's another way to find communities or "sublemmies" or whatever. Basically I see, I comment, I post, and I hope to find things related to my hobbies.
A little bit. What I hate is losing the communities related to my hobbies. Reddit is/was very very helpful for me. Finding new music, finding new games, discussing movies and TV, learning about weird movies or cult shows, sharing my stuff to people that find it cool... It was 11 years of that. I needed that site, so many very helpful posts. I hope whatever comes next is better. For now I'm here, waiting to see what happens.