I’m gonna try and answer your questions one by one

Let me preface with the fediverse pyramid. It goes projects (like Lemmy, mastodon, kbin which is what you’re on, etc). Then on all of these are instances which are like micro websites / servers. These instances host communities. You make your account on an instance which hosts all your information and posts, but you can interact with other instances

YES you can follow any community that’s made inside of an instance that isn’t your own. You’re on kbin so I’m not sure exactly how that looks for you but if I wanted to sub to this community for example I would put !youshouldknow@lemmy.world in the search bar

Federation is what allows these separate instances to talk to each other. If a community and another community have interests that directly counter each other, one might defederate with another. That means that if your account is hosted on one you can’t interact with the other. Accounts that aren’t on either are unaffected

No. Especially if they’re on the same project. I made this mistake too lol. Some projects are not able to post onto other projects right now, mostly because they update separately so sometimes they fall out of sync. Right now Lemmy users can’t make a post to mastodon, but mastodon users can post to Lemmy. I think kbin users can post to both

Also no, sorry. You’ll have to delete those extra accounts ^^; if you want to have different formated accounts (like how kbin has a magazine and Mastodon has a blog) you can’t link them. Personally I think of it like having a reddit account and a Twitter

Yes, you just have to search for the group like I said in response to question one

Any follow up questions just ask