SP - Golf Swing Training Aid

I have never heard of golf swing training aids in my life. Well, since I don't keep abreast about sports at all..

But hey, the term looks interesting enough. Initially, I thought it was some sort of device that helps with back problems caused by swinging the golf clubs. (I feel dumbed down because I thought of that..)

However, it seems like they are videos or some sort of guide that teaches you how to swing properly and use the right muscles and shit. Like a recipe book. And that website I just browsed is dodgy as hell.