The GeForce Tweak Utility FAQ can be
found in the GTU helpfile, which you can access at Start Menu -> Programs ->
GeForce Tweak Utility -> GTU Help when you've installed the full GTU
package.
How to use the helpfile:
Klick this button

and then click on a setting
under the System / Direct3D / OpenGL tab.

You will also find this on
several tabs:

Press it to get more information about the whole feature this tab represents.