Its a small disk shape button that goes just above your nock.When at full draw u place it in the corner of your mouth.It helps with your anchor point so that every time you draw u do the same thing each time ,it improves your accuracy.I place my thumb below my Jaw so I do the same thing each time.Do u need one ?Maybe?If you are having accuracy problems it would help.But they do slow your arrow speed down,about 4 t0 6 fps.