How categories work
See here for detailed lists of on Cookipedia's categories, for more general information on use of categories, read on.
The text below is unashamedly taken from the MediaWiki help pages.
A MediaWiki allows you to categorise pages by appending one or more Category tags to the content text. Adding these tags creates links at the bottom of the article which take you to the list of all pages in that category, which makes it easy to browse related articles.
How to make a Category
A Category will be created when you use that name as a link at the bottom of the page as explained next. It will not show, however, until the first linking page is Saved. Before that, it will show as an empty link in red; afterwards, it will begin automatically compiling a Contents page of all such linking pages.
You should be even more careful about doing this than adding content pages. Like content pages, Categories cannot be deleted or renamed, remaining to confuse users browsing the list of Categories. Before attempting to make a Category, please find the list of all Categories by clicking on "Special pages" in the left sidebar "toolbox" box. Check the contents of any other category that might suggest the one you had in mind.
How to add a page to a Category
To add a content page to the listing for a Category, simply put the following at the very bottom of the page you are editing:
[[Category:NAME]]
where "NAME" is the name of the Category you want to add it to. Any number of Category tags may be added to the page -- the page will be listed in all of them.
You can also specify an additional SORT parameter that specifies where the page will appear, alphabetically, within the Category. This is done by using the following markup:
[[Category:NAME|SORT]]
To add this page to the 'Help' category to be located in the list at 'C' you would use:
[[Category:Help|Categories]]
Without this, the page would be listed under 'H' for 'Help:Categories', instead of under 'C'. Another example is when you have articles about people that are titled as FirstName LastName but within a particular Category you want them listed as LastName, FirstName.
The SORT parameter does not affect how the page title is displayed in the Category listing, only how it is ordered in the list. In the above example, the link to this page at 'C' will still read "Help:Categories".
Another way to sort an article in the correct letter group without using the 'namespace' is:
[[Category:Help|{{SUBPAGENAME}}]]
This is helpful when using templates which include a category tag.
Linking to Category Pages
To create a link within page content, use a leading colon as in
[[:Category:NAME]]
so that "NAME" is the Category for the link. For example, if the name were "Help" the link would look like Category:Help. Without the leading colon, it would be instead blank or red in the text, because there is no such content page linked within that category.
If you want to display alternate text for the link, add that after a bar as with other internal links:
[[:Category:NAME|TEXT]]
The same link to Category:Help as above might show this alternative text: MediaWiki Help Index
Categorise Categories
Categories themselves and other uploaded files like images can be categorised like content pages. It is useful to connect the article-categories with categories already in place to establish connections and hierarchies. After saving the article, follow the category links at the end of the page to see if the Category is already in place and if not, categorise them until you connect them with an existing category.
Moving categories
Categories cannot be easily moved like other pages. For this reason, category names should be chosen carefully.
Those with admin privileges can create the new page, delete the old one, and then change the Category tags in each member of the category (manually or with a bot). However, this loses the page History - not a huge problem when categories are used only for navigation. But when a wiki is structured so that the category pages contain significant amounts of text, this is undesirable.
Moving with revision history
However, category pages can be moved together with the full revision history, with some effort, by using the Special:Export and Special:Import functions.