Lemmy and kbin are two different forum software that can be installed and run on servers. Because both use the ActivityPub protocol, the content between them can be shared. So, a Lemmy user will be able to see content from a server running kbin, using Lemmy.

But how can I see kbin content from lemmy, I couldnt find an option yet. Also from kbin I cannot find lemmy communities

This is due to Kbin using Cloudflare anti DDoS, which disallows Lemmy instances reaching it

That seems to go against the goal of federation.

Indeed, but my guess is that Kbin's admins don't really know. Also that's what I've read, it may very well not be that :p