The Function (FN) Key

To use the F1 though F12 keys as F1-F12 instead of changing the brightness or volume, hold down the Fn key and press the F-Key you wish to use. If you want to swap this (making it so you have to press the Fn key to adjust your light and sound settings) go to the apple in the top left, select System Preferences, click Keyboard and Mouse, click the keyboard tab at the top and check the "Use all F1, F2,..." check box.

To use the F1 though F12 keys as F1-F12 instead of changing the brightness or volume, hold down the Fn key and press the desired F-Key. If you wish to swap this (making it so you have to press the Fn key to adjust your light and sound settings) right click the Boot Camp icon in the bottom right, select keyboard then check the option to use the F-Keys as you desire.

In Windows, if you are still having trouble either changing the brightness, or using the FN key, please visit our answer on how to change the capabilities of the Function keys in Windows 7.