how I sign up to mastodon instances and whatnot with kbin

As I understand it, you don't sign up to a mastodon instance with kbin. Rather, kbin has the ability to act as a way of following fediverse users and hashtags in the same way as mastodon does.

In other words, if mastodon is the fediverse's version of twitter, and lemmy is the fediverse's version of reddit, then kbin is a combination of the two.

However, while kbin's lemmy/reddit features are maturing nicely, the mastodon/twitter functions are still pretty embryonic. (Bear in mind that kbin is a young project that for most of its life had only a single developer.)

For example:

• On kbin you can follow fediverse users by clicking on the "Follow" button in their profile (similar to the way you can follow users on mastodon), but I don't think there's a way of having their posts appear on a timeline yet.
• Similarly, while you can create a magazine that follows certain hashtags in the "microblog" section of a magazine, you can't currently do that as part of your kbin personal profile in the way you can choose to follow hashtags on mastodon and have them appear in your feed. (And the propagation of hashtags between kbin and the wider fediverse seems to be haphazard at the moment in any case.)

What I would recommend for now is to create a mastodon account on a mastodon instance of your choice, and treat the two ecoystems as largely independent, until kbin's feature set matures.