> Can one join many instances and, if so, does that mean what you post in one instance is not seen on others? Or does everything you do show up on your profile?
You can be registered on different instances, but they're all different accounts. The Fediverse "only" allows instances to share content with each other.
> This part confused me a bit. Can anyone ELI5?
If Mastodon instances A and B are connected through the Fediverse, you can _read_ content posted on B if you're registered on A.
The best analogy I've seen is to consider Fediverse servers like e-mail servers. You can post an e-mail from a server only if you have an account on it, but you can receive e-mails from any server.
You can be registered on different instances, but they're all different accounts. The Fediverse "only" allows instances to share content with each other.
> This part confused me a bit. Can anyone ELI5?
If Mastodon instances A and B are connected through the Fediverse, you can _read_ content posted on B if you're registered on A.
The best analogy I've seen is to consider Fediverse servers like e-mail servers. You can post an e-mail from a server only if you have an account on it, but you can receive e-mails from any server.