Okay, here goes. I was confused at first, so maybe my explanation will be more relatable than some of the others.
Let’s pretend there are three different websites: reddit.com, feddit.com, and seddit.com. Each one has its own subreddits:
These three websites can browse ALL of the other sites’ subreddits. On reddit.com you can browse and comment reddit.com/r/funny, feddit.com/r/funny, and seddit.com/r/funny, even though these three subreddits are entirely different from each other and not linked in any way. These subreddits are known as communities. Now it doesn’t matter whether you sign up on reddit, feddit, or seddit, since they can all browse ALL of the communities.
Now to expand on that just a tad: reddit, feddit, and seddit will still have their own rules, permissions, and such since they’re independent of each other. These distinguishing factors are (as far as I know) the only reason to choose one over another. Maybe server speed and some other factors.
The usernames reflect where you signed up. If I signed up on feddit, my username would be [email protected]
Hope that helps. I’ve found that once you understand lemmy, the explanations are more complicated than the actual setup itself.
Can this even happen while they’re at war with Russia?