[Explain] Somebody please explain to me in exactly 100 words how lemmy and kbin can share content if they're not the same.

As I understand it, it goes something like this:

1. You are on lemmy.cafe and ask to follow cats@kbin.org.
2. lemmy.cafe asks to follow cats@kbin.org
3. kbin.org makes a note to update lemmy.cafe every time someone posts to the cats magazine (but not previous posts).
4. Someone else on lemmy.cafe looks at the 'global' feed.
5. lemmy.cafe shows the cats@kbin.org posts, along with all the other remote posts that were requested, and all the local posts.
6. You upvote a cute cat post.
7. kbin.org interprets this as a 'like' (or whatever)

The language these services share is called 'ActivityPub'.