Lemmy and kbin are two different platforms, but are both on the ActivityPub network so they have access to the same content. Imagine if Reddit and Facebook were connected and anything posted to a Facebook group was viewable on Reddit as a subreddit with the same name as the Facebook group. You post to one, and it immediately shows up on the other. That’s basically what’s happening here between Lemmy and kbin. If someone makes a community on Lemmy, you can search for it on kbin as a magazine. The names are different depending on which platform you use (say, Facebook Group vs Subreddit - same thing, different name), but the content and comments are identical. What’s great about the ActivityPub network is that you can use any server/platform on its network and it’s all the same.

I use kbin because I find its layout a bit nicer than Lemmys, but that’s personal choice. If I decided to switch to Lemmy, I could subscribe to the exact same communities there as here. There is no functional difference between the content on kbin and Lemmy regarding community/magazine. kbin also has the added benefit of working with Mastodon which is a Twitter-like service that is also on ActivityPub, so everything is shared between that and kbin too (called microblog on kbin). I don’t really do the Twitter thing so that’s not really interesting to me, but it’s cool that kbin can do both Lemmy communities and Mastodon Toots from a single platform.

kbin also seems to work pretty well in mobile browsers, but I haven’t tried commenting or anything so there could be issues I don’t know about. Eventually getting an app would be nice, but for casual scrolling I don’t find using it in a browser to be very objectionable. Hopefully all that makes sense to you.