I am new to the Fediverse. I vaguely understand how Lemmy instances broadcast content to each other, but I was surprised to find Lemmy communities on kbin. How does that work?

And it also seems that mastodon can also be "syndicated" to these other communities, and vice versa? Is that true?

Are there limitations to any of this?

Apologies if this is not the perfect place to ask this question. I'm a lost old man. :-)