The feature you are referring to on your camera is called bracketing. On my D80 it is a small button that had BKT on it on the side on the camera. On my fujifilm S700 it is a symbol that looks like a camera with others beneath it. It differs from camera to camera but it is on most digital cameras.

This is the symbol on the D80.

It is the small button near the top on the side in the last picture.

This is the symbol on the Fujifilm S700.

It is the small button with the camera on it near the rear of the camera on the top.