kbin is part of the federation - like Lemmy - but it is coded differently and has a different developer. Since it is part of the federation, though, Lemmy users can subscribe to kbin communities (called magazines) and vice versa. kbin has threads like Lemmy, but it also has a micro blogging option similar to Twitter/Mastodon.
It's bugging out right now, probably because of the massive amount of traffic, but once things calm down you should be able to search for a magazine by full URL (https://kbin.social/m/gaming, for example) in communities, switch all search settings to "All", wait for your instance to pull in the magazine and click through to the federated URL (should look like https://lemmy.world/c/gaming@kbin.social, assuming you're on lemmy.world)
Basically, just like adding a community nobody else on your instance has added before.