>>375411369
People can do instance of worlds (that are user created content), most of the times things are unorganized and people join on others.
For other regular things such as dance session, movie watching, mahjong, ... people announce it in advance in the thread then post a link to join it, which is basically just a link to a world instance
If you are interested just join from the links eventually posted here or if there's none, ask if there's anything going on, you'll see it's way easier than it seems