Note that Rule Book is an add-on for Wardrobe, i.e., you must own the Wardrobe to be able to use the Rule Book.
After unpacking, make sure that you're wearing the Wardrobe HUD, then simply wear the Wardrobe Rule Book object.
This will start the installation of Rule Book into your Wardrobe HUD. When done, it will tell you that you can take it off.
That is all there is to it. If you get a new Wardrobe HUD, wear the Wardrobe Rulebook again to install it to your new HUD.