You're on street(ActivityPub), you have your home(lemmy.ml) and in your home there's a bunch of rooms with people hanging out(communities), but you can visit other houses(Beehaw, kbin) on the street and hang out in their rooms too.
There may be rooms in different houses that have similar purposes, but you can freely go to whichever is best for you and aren't required to stay home. It doesn't matter if there are multiple rooms in different houses for the same purpose; just check them out and see which one works best for you