It's the same thing as different subreddits with the same topic but slightly different names. Nothing special.

it does matter. they are technically managed by their local isntance, and do not share content. usually one will become 'popular' until the mods shit themselves, and everyone moves to a different instance. its one of the benefits of the 'verse

on some platforms, like my mbin instance links shared between communities are aggregated so you can view which one is getting the most activity

It's a pain in the butt. When people post, they often post to all of the communities, which fragments conversation - at least I think it does, since posts aren't shared across communities/instances.

But it's fine. If users are active, typically one community will be much larger than the others.

I wanted to add to others' comments: usernames as well.

So e.g. I could go create an account called Matty@lemmy.world, and another called Matty@lemm.ee, and another Matty@lemmy.zip, etc. (assuming none of these already existed), and they each would be different - plus none of these would be you.

This is a reason why many celebrities say that they refuse to come to the Fediverse, b/c of this potential for misunderstanding regarding the account names - which tbf that is not entirely "new" issue since it would affect emails too, and yet in reality it is new b/c Twitter/X and Reddit and Facebook got people spoiled to expect a certain style of behavior so using the Fediverse feels to them a step backwards (we had a discussion about that topic recently).

So, exactly like email and a website URL, it takes the full thing to specify something exactly - a username, or a community.

I changed how i look at communities when i switched to lemmy. Instead of just looking at the part before the @ i look at the whole thing and consider that to be its name.

So instead of the gaming community its gaming@xyz.qr and gaming@abc.de as a whole.

Tl;dr: theyre different separate comminities and the name is for all intents and purposes the entire thing.

I suggest subscribing to all of them for the topics you want and slowly through exposure learning which ones youd like to keep.

They're separate. You can treat them as alternative subs.

When I read, I subscribe to all alternatives on a topic I care about - e.g. Android. Then browsing the Subscribed fees would show me posts from all of them.

When I post, I check their user/month count in order to decide which one to post to. If I'm posting something important, I'd cross post it to the others, just like people do to similar alternative subreddits.