Help:Categories

A category is a page that has a list of links to all of the articles in that category. You can put pages into a category by putting something like this at the bottom of the page:

[[Category:Swimming]]

That would appear as a box at the bottom of the page that you want to put in the swimming category. The box would have a link in it to the category page. You can see and example of this at the bottom of the duck page.