A lot of people use the email analogy. So, there’s a different instances with different names. Each instance has communities like “news@lemmy.world” and “news@lemmy.ml”. My account is on another instance from those two, but I can see communities from all other instances. Unless their instance blocked mine, at which point their users cannot interact with me, and I can’t see their posts.

So, if you’re looking for “news”, you can look up that work in the community search and sub to multiple ones. The down side is you’ll often see duplicate posts. I hope they figure out a way to combine posts. But idk how they could automate that process without it becoming a shitshow. The up side is that if lemmy.world goes down, you can still access the rest of the “federation”. Unless your account was on the instance that went down. That’s another thing I wish could be solved.