There's no buttons or on-screen controls for the LED Cinema Display, all settings have to be made via software (brightness, contrast adjustment and so on). Apple does not supply any native windows utility for this, only one for use with Bootcamp, which is used to run Windows on a Mac computer.
It's not possible to install Bootcamp on a non-Apple computer, so you either have to live with not having any adjustments for your display, or you will have to jump through some hoops to extract the relevant exe from the software installer and manually put that on your PC's harddrive. Instructions on how to do this is available in some other thread I saw here a couple weeks ago...
It's not terribly complicated if you just have the right instructions, but it's more work than just buying a regular monitor and plugging that into your PC. This really is an Apple display, intended for Apple computers even though it does work on PCs too.