The servers (instances) aspect and different communities (forums on topics) on different servers and servers blocking others, is a mess if I’m being honest. It’s the biggest flaw. I still find it hard to find communities of topics I want…

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!