I am just getting into golf and have been out a few times. I picked up golf for dummies and a couple other books.
As I understand it I should keep my left arm straight and rotate on the back swing until my left shoulder points at the ball or ideally at my right foot and my back is to the target.
Well I have tried to do this and after a lot of stretching I just can’t get the rotation I think I need without wrenching my back. I have seen it done and pro golfers must be contortionists or something… I have to ask. Is this right? How can I get my back more limber, stretches etc.

Thanks!