Place one foot on box. Stand up onto box by pushing up with the front leg once leg is fully extended place foot of second leg on box. Step down with second leg by bending the knee of the front leg. Keep the front leg on the box.
Repeat until you reach desired reps then switch legs.
Note: Try and Maintain a good posture through the full range of movement. Once box is above knee height you start loading more glutes and hamstrings over quadriceps.