This is the root category of the wiki. All the others categories should be subcategories of another category, and every article should be in at least one category.
The Content category is intended for all articles about the subject matter of the wiki, whilst the Organization category is intended for all administrative matters.
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.
A full list of existing categories can be found at Special:Categories.