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"
“ This category may include pages and subcategories related to the active contributors to the...
“ To display all parents click on the "►": [+] Birds by letter To display all subcategories click...
Species by letter
“ 7 articles/subcategories in this category [−] Taxons that are complete [+] Families that are...
Taxons that are complete