Reddit

I'll try to be brief here, but IDK.... It's a bit much to summarize without waving my hands around and saying "it's magic".

So, the first thing I want to explain is the idea behind federation. Federating (at least in technological terms) in the simplest way is a method to make someone's login work somewhere else, like when you log into a website or a retailers webpage and you can either make an account with them, or "login using" then options for another site like Google or Facebook (or Twitter, or something.... The list is long for what options might be there). If you make an account using your email, it's unique to that site, but if you log in with, say, your Facebook or Google account, your access is federated. Basically the site pushes you to a Google login, you do so and approve it, and Google gives your browser a token (inside a cookie), the browser takes that token, validates it with Google, who sends key details to uniquely identify you as the person who signed in.

Your login isn't with that site specifically, but it works for that site. You are a federated user.

Lemmy is federated among itself. While there's a ton of "clones" (which are actually instances of Lemmy), they are all federated together, so your login to Lemmy.ml or whatever, works for getting you access to Lemmy.world, and Lemmy.ca and on and on and on.

Unless an instance is defederated, which is to remove access from non-local accounts, your login to whatever instance you signed up for, will work across all Lemmy "clones" as you say.

On top of that, there's sync and sharing of communities among Lemmy instances, so if you want to browse a community from Lemmy.world on Lemmy.ml or something, and your .ml login is subscribed to it, then your local instance will retrieve a copy of the community from .world for you (and others in your local instance) to browse.... Those communities are still on the source Lemmy instance, and when you post, your comment is replicated back to the original instance where the community lives and as long as your federated login is permitted to do so, the post will appear for other users across all federated Lemmy instances.

This is a basic tenant of decentralisation, so if one instance dies for any reason, it can be stood back up and all content can be re-replicated to it.... All federated Lemmy instances can work together to make sure nothing is lost.

It's confusing, I know but it is what it is.

TL;DR: your local Lemmy login permits you access to all federated Lemmy servers (you don't need a login to each one you want to use), and your "home" server will facilitate any posts you make to other servers communities, and bring you the content from those servers.