How to make a category in Radio

I’ve just posted (in reverse order *phew* so you can read it in the right order) a six-step tutorial explaining to Salon bloggers how to set up a new category in Radio so they can participate in the Salon blogs salon I’m trying to set up.
If you change the names of the categories and ignore the greater context (creating a multiauthor channel by subscribing to multiple feeds in an aggregator and posting them to a single category), the tutorial should explain making new categories for any Radio user reasonably well.
To check it out, you can start with Step 1. Peeking under the hood (just a little).