Hello Anne,
Thanks for answering, Schnee
You're quite welcome!
So when I click on it, I see a page that lists all the pages in the category, with an empty edit panel. What is it expecting me to add to that page? Is there some documentation other than Help:Category? I'm still studying that, but so far haven't found anything that explains this. I thought it was just the dynamically created list.
Categories are dynamically created lists, yes, but they're still pages as well, and you can add content to them just like you would to any other page.
For example, take Category:Mathematics on the English Wikipedia[1]; there is a list of sub-categories on that page, as well as a list of articles, but there's also some text above that, a link to the Mathematics portal and a link to the Wikimedia Commons for media files related to mathematics, and - last not least - a number of category links for categories that the Mathematics category is a sub-category of, such as Category:Logic, Category:Structure and others.
What you put on a category page is really up to you, but making a category part of another category is pretty standard, I think, and helps establish a hierarchy of categories.
I'm not sure if there's any further documentation, but the English Wikipedia's project page on categorization[2] might be helpful, although chances are parts of it will be specific to Wikipedia.
1. https://secure.wikimedia.org/wikipedia/en/wiki/Category%3AMathematics 2. https://secure.wikimedia.org/wikipedia/en/wiki/Wikipedia%3ACategorization