Help:Categories

Categories are pages that group together pages which share similar purposes, subjects or other qualities. To add a page to a category, add it as a link at the bottom of the page. Some templates may also assign categories when added to a page.

Hidden categories are just that; categories usually not displayed on a page. This is done only for maintenance categories, like Category:Todo. To mark a category as hidden, add  on that category's page. To make the website show hidden categories for you, check the Show hidden categories box in Special:Preferences.

If you want to simply link to a category on a page, put a  at the start of the page name, like this:.

It may take some time for a page to appear or disappear from a category. Try adding  at the end of the URL to nudge the server to do it faster. The wait time may be even longer if assigned through a template.

Sorting keys
A sort key allows you to change where in a category a page is listed. To change a page's location, simply add a  after the category name, and then specify where to put it. A sorting key can be as specific as needed. To make a page be categorized under the Es, just add. See Wikipedia:WP:SORTKEY for more information and uses.