User blog comment:Twilight rocker/Categories:/@comment-1642927-20100927013108

At the bottom of the article there's a button to add categories. Start typing and the suggested categories come up. Don't add a category that doesn't exist. Nor add categories that aren't needed.

Or go to edit mode and at the bottom again there is a button to add categories at the bottom and do the same as I mentioned above. Let me know if you still have questions.