This posture is called Parivrtta Parsvakonasana in Sanskrit, and it is the sixth posture in the standing sequence of the Ashtanga Primary Series. It asks for open hips and some flexibility in the spine, which the earlier poses of the traditional sequence give you. All the standing postures in the Ashtanga series are linked together.
This video breaks the posture down and shows you how to enter it step by step.
