This is a great exercise, one of my favourites! It works your obliques, shoulders, wrists, glutes and quads.
Start by placing yourself in a plank position like in the picture below:
Then place your right hand in the middle of your mat and push your hips up. Your body should be in a straight line from your head to your heels. Extend your left arm above your shoulder. Look up at your left palm and hold like in the picture below:
Then place your left arm under your body tuning your upper body to the right like the picture below:
If this is too hard for you to hold you can come down onto your elbow. Do 6-8 twists on each side 2-3 sets. If this exercise is too challenging just do what you can. The more you practice the stronger you will become. Tip: Engage your whole core by sucking your belly button in. This will help with holding the pose and to balance.