What is a category?
Categories are used to group and search for pages.
Page authors can put links to a category or categories on their pages. Then all pages of a given category can then be found by searching for the references to that category (pressing the title of the category page).
How do I assign a category to a page?
To mark a page as being part of a particular category you simply include a link to the category name, traditionally at the bottom of the page after a line. This is always a word beginning with Category. For instance, to make your home page part of the CategoryHomePage, you simply end your page with a line and then a link to CategoryHomePage. If you're not sure how to do this, check out the TextFormattingRules.
What categories exist?
See CategoryCategory for a list of all categories.
How do I create a new category?
Copy an existing category page, and change the name. Remember to add a link to CategoryCategory at the bottom of the category page. Edit CategoryCategory to show the newly created category in its proper context. (This shouldn't be too hard to figure out based on similar category names.)
Are there conventions I should know about?
A defunct feature of Wiki is discussed in CategorizedRecentChangesDiscussion.
Further discussion can be found on CategoriesDiscussion.
See also: WikiCategories