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.
Pages in category "Browse"
“ Why is it that speed from steam engines doesn't stack with default speed? Because ships are...
“ This category contains disambiguation pages — navigational aids which list other pages that...
“ For a full list of help pages, see Help:Contents, which includes help pages shared across Wikia.