This page is a category.
To add an existing page to a category:
3. your page is now listed in that category page!
See MozillaWiki:Categories for an overview.
This page should have relatively few entries in it, for ease of navigation.
Every category page can serve as alternate top level category for the corresponding subset of pages. Try to keep the number of categories listed here low, but if you have a nifty alternate way to categorize, look for an existing alternative subtop level that fits, as a last resort, make your own.
Every category should have a parent (except this one), if not anything else than this category.