Begin by positioning a barbell at or just below shoulder level in the squat rack. Behind the squat rack, place a box. Place yourself underneath the barbell. Make sure the bar is across your upper traps and not on your neck. Feet should be just wider than shoulder-width with your toes slightly turned out. Brace your core and keep your chest up. Bending at the knees, drive your hips back and down. Lower slowly with control until your glutes touch the box, inhaling as you do so. Pause at the bottom, then extend your legs and drive your hips forward to return to the start position, exhaling as you do so.