This is a great way to work your lower body if you do not have access to a squat rack. This movement will also build explosive power, which is great for athletes.
Begin by taking a stance that is approximately shoulder width apart. Hold your arms to your side. Next, squat down by pushing your hips back and bending through your knees. Squat down until your thighs are parallel to the floor. Next, push through your heel and then the ball of your foot to force your body into the air. You should use your thighs and calves like a spring to jump as high as you can. Once your body returns to the floor, you should squat down again and repeat the movement until your set is complete.
Once you have mastered this movement you can make it more difficult by placing a barbell across your back and performing the same motion. This can be very stressful on your body, so it is for advanced lifters only.
Be careful when your body is returning to the floor, landing wrong can cause injury. Control your body throughout the movement.