Piece of advice from someone experienced with federated social networks:
*Every instance will have it's own rules and communities. Check that first to see if it's for you and respect those rules.
*Not every instance connects with all of them. Check that too.
*Some instances will have technical limits, mostly because they're run voluntarily or made for small groups. If you can, support the admins.
*You can find information about the above on home/sign up/faq pages. Read first.
*Be kind and enjoy!
@ahmetasabanci are there other federated social networks?

@Kaitlin yes, one of the big ones back then was Diaspora (more Facebook like) and StatusNet (Twitter like). StatusNet became GNU Social and Mastodon is created based on that. Also one of the creators and admin of most famous StatusNet site idetin.ca then created something called pump.io.

There's quite a messy history out there :)