Position barbell on back of shoulders and grasp bar to sides.
Keeping back straight, bend hips to lower torso forward until parallel to floor. Bend knees slightly during descent. Raise torso until hips are extended. Repeat.
Begin with very light weight and add additional weight gradually to allow adequate adaptation. Throughout lift, keep back straight. Knees will have to bend more with those with less hamstring flexibility. Knees can be kept bent throughout movement. Also see straight leg Goodmorning emphasizing Hamstrings.