All categories need to be added to this category. This is the home for all categories and sub-categories, and sub-sub-categories and so on.
To add a new category to a page you can click the Category button at the bottom of the page and type in the name you'd like your category to be called. Then hit return and then hit the save button.
Please note, that naming a category does not "create" it. To actually make it active, you need to open the category page, click the "Create" button, then type something on the page. It also must be put in a category and/or a sub-category, as many as apply. Please make sure that one of those categories is the "Browse" category. Pages and categories not assigned to an active category become lost, floating in wiki space, so to speak.
A full list of existing categories can be found at Special:Categories.
This category has the following 69 subcategories, out of 69 total.