Instructions
Place a barbell on your back, either by picking it up off the floor or from a squat rack. Stand up tall and take a wide stance where your feet are at least twice the distance of your shoulders and flare your toes out slightly. Shift your weight over to one foot and bend your hips and knees downward, allowing your knees to travel over your toes on this leg. At the same time draw the toes of the opposite leg upwards, keeping that leg straight. Once you get as low as you can, drive into the foot on the bent leg and stand back up to the starting position. Without adjusting your feet, repeat on the opposite side, then repeat for the desired number of repetitions.
Tips
Your torso should be kept upright throughout the whole movement. To help with this, think about pushing your hips down and not back behind you. You shouldn't feel any pain in your hips, knees, or ankles. If you do, then you might have gone passed your natural mobility limits. Only go as low as your mobility allows and work on getting lower over time. You can also adjust your stance (narrower or wider) to see if you can get lower. If you are limited by mobility, work on this exercise with just your bodyweight.
This exercise can also be performed by doing the required number of repetitions on one side, followed by the other side.