Hi!
Since you're on Lemmy, I'll explain the part of the fediverse that I know best. The best way I can articulate it based on what I know is this... it's a bunch of different sites, using the same software, known as Lemmy. Each site using the Lemmy software is called an instance, and these instances are able to correspond in a way that is pretty seamless as if it's all one big site! Although you never actually leave your native instance, it doesn't feel that way because when you post to an instance that isn't your native one, it's like sending a request to that instance to push your post forward. In no time, your post appears on the remote instance!
One of the best things about this is each instance is independently operated, so you don't have to worry about a rogue admin making unfavourable changes. For instance (hehe) I'm on the lemm.ee instance, but I'm posting to Ask Lemmy@lemmy.world via this page! lemm.ee/post/62441272