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.
This category has the following 23 subcategories, out of 23 total.
Pages in category "Browse"
The following 200 pages are in this category, out of 200 total.
Media in category "Browse"
This category contains only the following file.