What can I do with my kbin logon besides veiw kbin and lemmy?

You can interact with Mastodon (a microblogging site like Twitter) via the microblog tab. By going to the All page and then clicking Microblog, you'll see everything that Mastodon sites share with kbin.social (and vice versa).

Individual Kbin magazines work a bit differently. A magazine's microblog tab only contains:

• what people on Kbin post to that magazine's microblog tab
• any microblogs (e.g., Mastodon posts) that have certain tags

Each magazine can set which tags its microblog tab will collect. For example, @pixelart has microblogs with the #pixelart tag. This is nice if you only want microblogs on a specific topic, but if you want to browse everything that Mastodon shares with Kbin, you'll need to use the All page (and make sure that you have federation turned on).

EDIT: Reworded to be a bit clearer

Generally with most Fediverse applications, the idea is that since they all "speak" ActivityPub, that you're supposed to be able to subscribe to content from other applications from your account/instance. In practice the results may vary (I haven't used Kbin so I don't know what it does and doesn't support), but your Kbin login will only work on kbin.social, since logins themselves aren't federated.

I'm not an expert, but I think kbin could implement UI to allow you to view events (things) from those other instances.

I assume right now kbin is only looking at a handful of the types of stuff that can be shared in the fediverse.

At least, that's my layman's understanding right now.

You can also interact with Mastodon.