They're meant to be used with Flexbar, which doesn't have any graphics to speak of on its own. That way you can move your flexbar buttons around on top of these graphical bits, and have a nice looking and functional UI.
You can get flexbar
here - there is a "flexbar for dummies.txt" file included with DiivSkins that should contain some tips for using flexbar, because it is very flexable, but that also makes it a bit intimidating when you start out using it.
Hope this helps!