I’m still sort of confused myself, but I think (someone please confirm or deny) a good non internet metaphor would be like a neighborhood or a small town. You move into Smallville, and you live, work, and shop there and become friends with a lot of the people there. That’s lemmy.world. It’s where you live. But there’s nothing stopping you from getting on a bus or in your car and going and visiting TinyTown and shopping or visiting the residents there (ie, interacting with other instances), and they can come to Smallville and interact with you. Beehaw is like Grumpytown, they decided they didn’t want to deal with certain people, so they built a wall around their town and blew up the bridges so no one can come visit and also their residents can’t get out.
Me reading this comment with my cat smushed against my head