This is a breakdown of how to do supported headstand. It can be a great pose but it can also be a little misleading - you want to keep as much weight off your head as possible! This is why I much prefer this version of headstand over a tripod headstand. I personally much prefer forearmstands and handstands (working on them!) over headstand (and shoulderstand - I rarely, if ever, go there nowadays) as I think they are much safer poses to practice if you like inversions.
However, headstand can be a lot more accessible than handstands and forearmstands and hence it is usually learnt first out of the three. Please note that when you first start learning this pose BE PATIENT and use a wall behind you - safety first guys! I cannot stress this next part enough - do not kick up - it's all in the core. So maybe you spent months at stage 2/3 - that's okay! With daily yoga practice (of any kind, not just headstands) you will build the overall strength in the core and the shoulders you need in order to lift the legs without kicking. One more time --- do not kick up!
Begin with your knees on the floor and take the time to measure out your arms. Grab for opposite arms, you should be wrapping your hands around. This makes sure that the elbows are beneath the shoulders. Make sure you keep the elbows where they are. Interlace the fingers or 'cup' the hands. I am very much of the belief that different things work for different people so have a play around and see what feels more comfortable. Place the crown of your head down to the floor as the back of the head comes into the hands. The hands are simply there for support and the head should simply rest in the hands.
Tuck your toes and lift your knees up off the floor. If this is your first time coming into this pose maybe that's where you stay for today. Press the forearms into the mat, draw the shoulder blades away from the neck and when you feel ready, slowly start to walk the feet in so that your hips stack over your shoulders. Keep pressing into the forearms and maybe lift one foot up to the sit bones. You should shift your weight forwards slightly so that the feet become light - remember no kicking or bouncing.
As you lift one foot off the floor make sure the knee is in towards the chest. When you feel ready, slowly lift the second foot off and hug both knees into the chest. You can stay in this little 'egg' shape and find your balance. When you are ready bring the hips over the shoulders completely and then start to extend the feet towards the sky.
Once you are in full headstand keep extending through the feet towards the sky, pushing into the forearms in order to keep as much weight off the head as possible and lengthen through the tail bone. Keep the core engaged by pulling the low belly in and remember to breathe! When you are ready to come down, come out the same way you came in, one leg at a time. Rest in child's pose.
If you would like me to breakdown a particular pose please let me know in the comments below.