With an elevated surface in front of you, place one of your feet on the platform so that your knee is roughly at a 90 degree bend.

Start by pushing through the foot of your raised leg until it's straightened. As you push up, bend your back leg upwards to balance yourself, hold briefly, then in a controlled manner lower yourself down by bending the raised leg back to a 90 degree bend. Ensure that you keep your head looking forward and have your shoulders back. Repeat for the desired amount of repetitions then swap legs.

Avoid jumping up and pushing through the back leg to make the exercise easier. You may also need to lower the height of the platform to perform the exercise with good form.