When you click on the 'All' tab on your home page, you must have noticed communities from other instances gets shown. The total number of communities on the fediverse is much higher than only the ones shown however, and to make a specific community visible, any 1 person in the instance needs to copy its link and search it from here and subscribe.

Once someone does that, the local db fetches that information which will make it visible for everyone in the server.

So if you find an interesting community outside of this server, make sure to search about it here so its posts gets shown here in the future.

I know this might be confusing, so feel free to ask questions about this or something else about Lemmy in the comments or in a seperate post. Cheers!