One of my former teachers in Austin, Sam Rice, wrote a blog post on it with great, detailed instructions...here is her beautiful pose:
This pose strengthens everything. And the strength is built not by doing this pose, but by trying with all your might to get your bum off the floor!
If you struggle to lift up, put a block underneath the foot of the straight leg + move your hands forward of your hips.
In my opinion, it is the best introductory arm balance when practice alongside Bakasana, which will get to eventually this year. If you want to start balancing on your hands, do this pose.