How user accounts work with the fediverse?? Can I sign in with my Fedia account on other Lemmy, Mbin etc instances?

At the moment they work like email addresses. You have an [email protected] account, you can only log into gmail.com’s server. But you can talk to [email protected], the fediverse (gmail.com and outlook.com’s servers) takes care of passing the messages / posts for you.

@[email protected] You can't log into other instances from your Fedia account. Not yet, at least. I know that account portability is something that many Fedi platforms are working on improving, so that could change in the future!