Stand upright, feet in a shoulder-width stance, hands on your hips.
Raise your leg by flexing your hip and knee upwards. Make sure that you are not bending your hip and knee to more than a 90-degree angle.
Stand on one leg and rotate the ankle of your raised leg. Repeat rotation several times to each side by alternating your legs.
Make sure you have the correct angle in both joints.
Stand upright with your torso straight.
Exercising in front of the mirror will allow you to check for correct motion.
While obviously not a mass builder, this is a perfect exercise for the beginning of calf workout. It is also well suited for people recovering from calf injury.