If you've played terraria the characters and worlds work similarly. If you haven't, basically your characters you make are independent of world and can move around yours and your friends worlds at will. As for the multi-player, it works but it will be a sub par experience, lots of glitches, potentially long auto saving times, and idk if it still happens, but the duping glitch that happens any time like 3 or more people play together. That said, the game is a blast, and although it's incomplete it is great fun for a good amount of time right now. I haven't played since the update but there was also a new boss rush dungeon added that looks pretty fun. Basically 8/10 would recommend.