Use function keys on a Mac keyboard in Windows with Boot Camp
In Windows on Mac, pressing function keys on a portable Mac and some other Apple keyboards controls hardware features. Boot Camp supports the volume, brightness, keyboard illumination, and media keys.
In the Boot Camp Control Panel, you can change the default behavior, so that pressing a function key controls app features, and pressing a function key and the Fn key controls hardware features.
In Windows on your Mac, click
in the right side of the taskbar, click the Boot Camp icon 
, then choose Boot Camp Control Panel.If a User Account Control dialog appears, click Yes.
Click Keyboard.
Select or deselect “Use all F1, F2 etc. keys as standard function keys.”
Some portable Mac computers have a group of keys with small numbers on them that can be used as a numeric keypad. To use these keys as a keypad, press the Num Lock (F6) key, or hold down the Fn key while you press the keys on the keyboard.