I dont’t know what’s so confusing about this. Just sign up for an instance who’s accepting new users after researching about what an instance is and finding one that’s not overbooked and is accepting new users and then once you’re on, just find new communities but also change the settings to “all” and then start a new community when what you wanted wasn’t there except there’s some sort of format error when you do that but it’s ok because the community you wanted was there all along it just wasn’t searchable because no one from your instance had searched for it/joined it yet. It seems pretty self-explanatory to me. Just don’t talk about the linking.