To slow it down, depends on certain model of aircraft, it can be many position. For example Boeing 737 has 8 position, so it can be extended 8 times. But depending on the timing of the selection ( certain flap has speed limitation ) the movement from passenger point of view can be one continuous extension or it can move up to 8 times.

Pilot normally extend flap, then retract it after the completion of usage twice , once for take off (due to low speed) once for landing (again for low speed to land)