You just make an account on a different instance. Lemmy instances are kind of like email providers. You can have a slickgoat@lemmy.world, slickgoat@lemmy.dbzer0.com, slickgoat@lemmy.ml, etc… Different instances will tend to have very different admin styles. You also still need to follow the rules for whatever local community you’re on as well. So using this thread as an example, I’m on lemmy.dbzer0.com but I still need to follow the local mod’s “no celebrating death” rule. As long as they’re federated with the same instances, you’ll be able to see all the same content.

lemmy.world tends to be many users’ first instance, simply because .world was one of the few instances that kept open registrations during the biggest Reddit migration. So it’s the largest, simply because it’s where most of the new users landed. But it is also frequently looked down on by other instances, because the .world mods tend to skew farther right than lots of Lemmy users prefer.

Mic check covered it nicely, you just make an account through that instances site.