Here's how:
- Find a bench or box that can be stepped up on
- Have a partner stand behind you with a bungee cord or some type of "stretchy" band around your waist
- With one foot on the box and one foot on the box, explosively drive into the air off of the elevated leg
- Land and repeat
Perform with the opposite leg.
Check out the video below to see it in action and for suggest sets and reps.