Stand with back of thighs or glutes against bar. Grasp bar from behind with overhand grip. Disengage bar by rotating bar back.
Squat down by bending knees forward slightly while allowing hips to bend back behind, keeping back straight and knees pointed same direction as feet. Descend until thighs are too close to parallel to floor and bar is behind lower leg. Lift bar by extending hips and knees to full extension. Repeat.
Throughout lift, keep hips low, shoulders high, arms and back straight. Knees should point same direction as feet throughout movement. See Smith Squat Analysis.