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. Categories are useful because someone could look at the swimming category page and see every article that has to do with swimming.