I love this federation! (Is that the right thing to say?)
It's technically called an instance (of Lemmy), but you can also call it a server, which is typically easier to understand for people unfamiliar with the platform.
I'm not really into any of the things you name dropped, but if you got guitar skills I think that's a pretty good thing to start a community around. Maybe just for guitar players in general, because beginner guitar help is too niche, the userbase prob can't support something like that yet.
If you're looking for communities to join, use browse.feddit.de to make it easier.
Welcome and glad to have you onboard!