Also, you can go to https://browse.feddit.de/ and find communities. If they're not available on your lemmy instance, you can copy+paste the URL into your lemmy instance's search field and as long as it's not blocked by the instance it will be federated from then on.
It's not the best experience and it's not obvious or intuitive. A browser extension could simplify it substantially, at least. As could new features in lemmy itself, but you want to be careful about every lemmy instance consuming the content from every other one, as that won't scale easily for the average lemmy admin.
If anyone is wondering it’s still not quite perfect as some instances have inadvertently blocked federation while they deal with growth. It should work itself out once the dust settles
