This light will come on briefly when you start the engine, then it will turn off. This is normal.
If the light stays on, or comes on when you are driving, your vehicle needs service. If the brake or low air warning light is not on, you still have brakes, but you do not have the antilock brake feature. If the brake and/or low air warning light is on, you do not have antilock brakes and there is a problem with your regular brakes. See Brake System Warning Light and Antilock Brake System (ABS) for more information.