How does a slingshot work?

Can you explain, in simple terms, the mechanics behind a slingshot and how it harnesses the power of elastic energy to propel a projectile? How does the user's action of pulling back the pouch and releasing it convert that energy into the speed and distance of the projectile? Are there any factors that affect the accuracy and power of a slingshot, such as the material of the pouch or the length of the arms?