Right now the user count Lemmys is comparatively tiny when held up against reddit - but the user count isn’t the thing that makes a social media site, it’s the engagement
So even if you’re used to lurking, try to get a little more active! Post memes, vote on posts, talk in the comments, whatever!
If people come here and see activity, content, and discussions, they’re more likely to stay and contribute their own - if they come and see a ghost town, they’ll just go back to reddit
Each instance has its own communities and they’re separate from each other. If someone created a /memes/ community on another instance it would be its own thing, but people from other instances would still be able to view it.
To view a community on another instance you’d have to put the instance name in the URL. For example, if there was an instance called “coolinstance.com” with a community called “stuff”, then for users on the coolinstance.com instance the URL for that community would be coolinstance.com/c/stuff. If there was another instance called reallycoolinstance.com, they’d still be able to see the “stuff” community, but to them the URL would be reallycoolinstance.com/c/stuff@coolinstance.com. They’d also be able to create their own “stuff” community, and people on coolinstance.com could access it by going to coolinstance.com/c/stuff@reallycoolinstance.com.