Thanks, so you can register with multiple servers (instances) right? Like I have a lemmy.world account and a Feddit.uk one, I am generally logged into the fedddit.uk. when would I need to switch over to using Lemmy.world? Do i need too?

Also can you only find certain communities depending on which account your signed into

Newbie here and apologies if these are FAQs but just want one line answers

What’s an instance?

What’s a community?

What are federations?

Whats the difference between all these?

What’s mastodon?

What’s Kbin?

What’s ActivityPub?

Just jargon I’m trying to get my head around, I’m still confused on signing up to different communities?! I guess and yeah… a bit lost I suppose. If there are FAQs to all this please direct me to them, thanks!