ELI5

Do 5 year olds have email? Because it's kind of like that. You have an email address "[email protected]" and you can send a message to "[email protected]". You don't both have to be on Gmail.

Well fediverse apps are kind of like this. Imagine lots of little reddits with their own communities and user bases.

You are [email protected]. You can talk to [email protected]. Same goes for magazines/communities (subreddits). If you want to join a magazine on another server, you can do that like @technology (notice the leading @ symbol which tells Kbin that it's a magazine and not a user).

This is what is most important for the average user to understand about the fediverse. There is a ton more than this like interoperability with different apps that aren't thread based like Kbin and Lemmy like Mastodon but that's a different discussion.

Edit: The community link should probably start with an ! as suggested by @fu but there is a known issue with formatting presently: https://codeberg.org/Kbin/kbin-core/issues/199