So.... First thing is first. Lemmy works on what they're calling the "fediverse" (don't ask me, I didn't name it). Effectively, each Lemmy server, like Lemmy.ca or Lemmy.world (or whatever) is independent. But, through the power/magic of the fediverse, you can post on servers that are not your local server, and people from other servers can see/comment on your posts.

Because of this, things get a bit fractured. You can have communities (you might refer to them as "subreddits"), that are named the same on different servers. Eg, "/c/memes" on several servers, and they're entirely disconnected from eachother. They have different subscriber bases and different content.

So it's like Reddit, but now everything is broken down per server as well.

You, personally, can choose to block a single user on a single server (also called an instance), or block that entire server, so you can't see any of their content or posts by any users on those servers. Some Lemmy instances are more politically left/right/center/neutral, others seem to be found on almost entirely Marxist ideals. Some are simply geographically centered (like lemmy.ca is, where I am, in Canada). You are not required, as far as I know, to live in the geography where a geographic Lemmy instance is, but it can help.

Other than that, there's not a lot that's different day to day. You post, people up/down vote your posts, you live and move on. There's a lot less emphasis of how many updoots or downdoots you have overall. Most servers don't even really tell you those stats about anyone but yourself. At least, that was the case the last time I looked.

One last note about the fediverse: there are other apps that use the same fediverse login stuff, so you may get cross over from other platforms. I don't really dabble in all of that, I just stick to my local instance and use it like I would use Reddit.

Welcome fellow lemming.