HOW: Place a step in front of a wall or an object to use for balance. Step onto the box with the balls of your feet on the edge of the box, and your heels off the box. While keeping your glutes and quads tight to keep your knees straight, lift your heels up in a slow and controlled manner, then slowly lower your heels back down to the ground. Repeat
FEEL: You should feel your calves getting a workout, but also your glutes and quads working as well to help keep your legs straight.
COMPENSATION: Do not let your knees bend as that is a different exercise. Do not shift your weight side to side. Make sure you go through your full range of motion at your ankle. This is not a balance exercise, so hold onto something to help with balance as the goal of this exercise is to strengthen your calves!