This is a great bum shaper! It is tough which is why I like it.
Start on all fours then slowly lift your left leg out to the side keeping it hip level and extend backwards, then bring it back to the side again and drop your leg back to starting position and repeat. Remember to always hold your leg hip level if you can. If you can’t do this in the beginning do not worry. Just do what you can. Do 16 repetitions 2-3 sets on each leg. If you can’t do 16 try to do 8.