Do not be intimidated by the Sirasana, which is the exact opposite of standing on our feet. If the feet can do it, why can’t the head!
The Sirasana is usually approached from Balasana (Child Pose) or Virasana (Hero Pose). It is important that the crown of the head be placed on the mat, and not the forehead for you want to create a straight vertical line from your head to your toes without putting unnecessary strain on your neck. Remember to place your forearms firmly on the mat and push your shoulders down as if lengthening your neck to come up to the full position. You will also find a set of strong abdominal muscles useful when lifting the legs off the ground.
It is natural to want to start out by using the wall, but do refrain from doing so as it only creates your dependency on this support system. Do not be afraid to fall as you will soon realise that your confidence increases with each fall.
A variation to the Sirasana is the Tripod. The difference is that a triangular three point support is created with the crown of your head, left and right palms. I find this pose easier to master as it generates a more stable support structure.
Some of the effects I have observed after practising the Sirasana is the clarity and serenity of mind that follows. It is also reputed to reduce heart strain and fatigue.