I think it works like this: each account belongs to an instance which is your home instance. You can go to other instances to interact with their communities, but your profile (where your history is) is on your home instance. The only difference I’ve notice is that, posting on your home instance then your post is just username, but on away instances it’s username@homeinstance. Otherwise it seems to work the exact same as interacting with communities on your home instance. But I’ve only just signed up so I am making guessing!

Tbf this is the sh.it just.works instance - some of the others a more hit and miss