To give you an brief idea how’s sarvangasana can be done, here I’ve included an article about sarvangasana from atoneyoga.

Sarvangasana is best done near the end a full practice. As an inversion it reverses the effects of gravity, decompresses the spine and helps re-align the arms with the shoulders. It also improves energy balance and metabolism by wringing out the thyroid and parathyroid glands in the throat.

A few cautions: Remember that this is a SHOULDER stand and not a neck-stand. Do not turn the head from side to side in the posture. Many teachers highly recommend beginners use folded blankets under the shoulders with the back of the head on the floor to help preserve a curved space beneath the lower neck. Avoid this posture during menstruation or bouts of hypertension.

Posture Points

• Elbows shoulder blade-width apart behind back. Use a blanket or maintain a thick pad of muscle and flesh below the shoulders.
• Legs together with balls of feet extending straight to ceiling
• Spine long and straight.
• Triceps and shoulder blades as close together as possible.
• Palms flat on kidneys, fingertips towards feet. Work heels of palms towards scapula.
• Legs together, draw navel-point in and reach tailbone towards heels.
• Always maintain a calm and even breath.

Sarvangasana: Two legs reach up as one, thighs and knees spiraling inward. Reach tailbone to heels.