How do i create an angry birds style slingshot on a 2d plane?

Trying to make a angry birds slingshot that pulls back and fires at different strengths depending on how fair it’s pulled back, any help?

You would do this using vectors. Vector magnitude would be the strength of the shot. The vector would be the angle or direction of the shot. A single vector is direction from 0,0,0 or you can take to vectors (which are essentially two points in space) and you can get a direction vector from those two points (location of the sling, and location of mouse pointer or whatever point would be where the end of the sling is)