To get into this pose, start in Tadasana and lightly jump your legs out to about your arms length. Next, pivot your right foot so it creates a ninety degree angle, and your left foot so it is about forty five degrees. Make sure that both of your feet are aligned. It is very important that throughout this pose your back foot remains firmed and raised. Support this foot by keeping your kneecap "up" by engaging your quadriceps. The next step in this process is to lower your pelvis so that your front knee is directly over your front ankle to create a right angle. You should then lift your rear foot until the weight is on the ball of this foot. Next position your hips so they are facing the direction of your front leg, as even as possible. You're almost there! Finally, you are going to start to move your torso down to your front leg. After lowering your ribcage to your bent front leg, you are going to engage the spine with a twist; now gently hooking your arm in the crook of your front, bent kneecap. Extend your arm to the floor for more leverage and try to reach your navel and torso open to the sky. Finally, position your right (/arm not touching the ground) straight over your head and move your gaze towards your hand and up to the sky. You are now in Parivrtta Parsvakonasana!
In this pose you will be activating our abdominal and core muscles, quadriceps, and others.