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 6 subcategories, out of 6 total.
Pages in category "Browse"
This category contains only the following page.
Blog articles in category "Browse"
There is one blog article in this category.