Adjust the padding so that when your standing on the floor, the shoulder padding is roughly at shoulder height. Then place your shoulders under the padding and step onto the platform, placing your feet roughly shoulder width apart on the platform. Position the balls of your feet on the platform so your heels are hanging off.
Steadily lower your heels downward until your calves feel fully stretched, then drive your heels back up as high as comfortable. You should feel the weight on the inside of the balls of your feet when performing the exercise. Repeat for the desired amount of repetitions then bend your knees slowly until the weights are caught.
Avoid using momentum to bounce up the weight and keep a neutral spine position throughout.