Use a rack such as a squat or power rack to hold the barbell. Place your feet shoulder width apart under the bar. Grasp the bar just wider then shoulder width, duck your head under the bar and position it on your trapezius muscles behind your neck. Lift the bar from the rack and take a few steps back. Position your feet shoulder width apart with your toes pointed just slightly out to the sides. Look forward and keep your head up.
Keep a slight bend in the knees and slowly lower your upper body until it is a little lower then a 45-degree angle with the floor. Then slowly lift your upper body back up to the starting position. Repeat.
Tip - use very light weights when starting out with this exercise and build up gradually, because it places a lot of stress on the lower back.
source: www.leehayward.com
