This is our top-level category; looking at it another way, it is not really a category at all! Oooh! Eastern Zen shit!
Ideally, every other category should be a subcategory of this one, but I guess you could be dick and put this in some made-up stupid Category like "Dorito-Blast Taco Shells" or something. You would, too, you fucker.
Most every Category is hierarchical to at least one other, and every article should be in at least one category; many will fit well into two or more (e.g. Events, Battles, and Comics Issues). They are like a special tree of life, spiritual and harmonious with Earthsong Treemother Gaia buttefly rainbow fuckstick. Some are orphans though, and cry themselves to sleep each night as they slowly starve in the cold. Many are in a feedback loop, or a constant battle for Category supremacy. You could just look at all of the Categories at once, and watch with a God's-eye-view from there as the little pissants bustle about with their sundry affairs and mortal matters. Laugh at them. Laugh, I say.
To add a new category to a page, just add
[[Category:Categoryname]] to the end of the article or existing category page. Have fun, but don't be too Goddamned ridiculous, or you'll end up having to clean out all the stupid extra Category detritus.