In order to take advantage of Nikon's CLS (creative lighting system) you
will need either an SB600, SB700, SB800 or SB900 (flash) and the pop up flash on your camera. You will set your on board flash to commander and your
speedlight to remote, thats it! Confused? Heres how to do it with a D300
and SB800. Menus should be really close with other D bodies but you can
check your manual for specifics.
On the camera, go to your custom setting menu