To do a barbell squat, start by positioning the barbell comfortably across your upper back, just below the neck, gripping it firmly with your hands slightly wider than shoulder-width apart. Stand with your feet about shoulder-width apart, toes slightly pointed out. Engage your core, keep your chest lifted, and maintain a neutral spine as you begin to lower your body by bending at the hips and knees simultaneously. Lower down until your thighs are at least parallel to the floor, or deeper if your mobility allows, while keeping your weight evenly distributed through your heels and mid-foot. Then, press through your heels to drive back up to a standing position, fully extending your hips and knees. Throughout the movement, keep your knees tracking over your toes and avoid letting your lower back round or your chest collapse.