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.
“ Hey guys, Killer Duck here and this is an update for the wiki. I would consider this wiki dead...
“ Pages in this category have been labelled for deletion. To add a page to this category, type...
Candidates for deletion
“ 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.