In the attached video you will find a step-by-step instructions for the Sarvangasana (Shoulderstand) Yoga asana. The video itself is generously commented with all the details about benefits of the yoga pose, it has variations from one for people who just starting the asana practice to the variation without arm support, full Shoulderstand. Many other details are discussed too: neck overstretch in the asana and it's prevention, massage of the hear muscles with more blood going down when body is in inverted Yoga pose, Shoulderstand as a substitute for the Headstand (Shirshasana), etc.
Leg raises in the Shoulderstand
The next video shows leg raises in the Shoulderstand. Leg raises (one after another or both legs together) help to develop lower back and abdomen muscles. These are two very important groups of muscles for your body - they are supporting you up-straight whole your life. If these muscles are underdeveloped sooner or later one will likely develop back problems. Plus in addition to simple exit from the Shoulderstand shown in the above, main video for the asana, exit by entering directly into the Bridge Yoga pose is shown.