How does an airplane use drag?

Gravity and drag are forces that an aircraft must continuously overcome in order to climb and maintain altitude. Without adequate thrust, they are the default operational forces operating on an aircraft. Those forces are always present. A pilot at altitude is able to use them to advantage by simply pulling out the throttle, which lowers the engine's output/thrust and lowers the lift of the wings. With insufficient thrust to create sufficient lift to overcome gravity and drag, the pilot then watches the aircraft descend to a lower, more desirable altitude. Some highspeed jets use airbrakes and dragchutes which add to the plane's drag and slow it down once it has landed.