This is the top-level category where all categories stem from. This category itself should remain uncategorized.
The "Content" subcategory is intended for all articles about the subject matter of the wiki, whilst "Organization" is intended for all administrative matters or wiki-related functions.
To add a new category to a page, just add
[[Category:Categoryname]] to the end of the article or existing category page. A full list of existing categories can be found at Special:Categories. You can also view categories by using Special:CategoryTree.