Toss game char how to throw the ball

In a nut shell I have made a toss game like the angry birds games. I have a model that I would like to move their arm back as you drag to shoot (aka like the slingshot) and let go to fire. How would I start to do this, anything even a starting point on what to read in order to learn this would help.
Thank you for your time :smile:

http://forum.unity3d.com/threads/86472-Drag-Shot-Mover-Get-your-physics-objects-moving!?highlight=slingshot