Vortex generators work by mixing high-energy fluid (free stream air in this case) with the lower energy fluid found near the skin surface, called the boundary layer. This process is called re-energizing the boundary layer. The higher energy fluid is now more resistant to separation and allows for higher performance of the aircraft. Technically speaking a vortex generator increases the mean streamwise momentum of the boundary layer by drawing in high momentum fluid from the free stream.
Vortex generators can be used to improve the performance of aircraft in a variety of ways. If properly sized and positioned vortex generators can be used to lower the stall speed of an aircraft, improve stability and control during maneuvering, decrease turning radius, decrease takeoff distance and increase takeoff weight. For commercial aircraft this can mean higher payloads and increased safety. While the general aviation pilot will enjoy better maneuverability as well as the increase in safety.