First you need to stand with your feet, shoulder-width apart, so you are balanced.
Lift your arms high in the air. It is important that you use your arms in a backbend so you do not injure yourself
Go down slowly and bend your back as far as you can without hurting yourself.
After your down(you will not get it the first time) place your feet and use your hips to pull yourself up.
Here is my Backbend with all the steps put together.