This is a great exercise for shaping your glutes. Start on all fours. Make sure your hands are parallel underneath your shoulders. Extend your right leg. The knee resting on the mat should be in line with your hip.
Extend your right leg and lift it up and then down flexing your foot. You should be feeling it in your glutes. You can also engage your abdominals. I do 2-3 sets of 40 on each leg. If this is too difficult start with 20. Just do what you can. You will get stronger the more you do this.