The only dumb questions are the ones that are never asked!
Yes you can use them w/ a string loop.
The primary function is to teach one to shoot with back tension so that you eliminate jerking/punching the trigger, cure target panic (at least temporarily), and ensures proper aiming techniques. It promotes a "surprise" release instead of a "command" release resulting in much better and more consistent accuracy once the technique is properly learned, however for some folks it's extremely difficult tograsp/learn that method of shooting. Some folks take to it ina few months, some take a few years, some never do.
I tried one several years ago, and it was an abysmal failure. However I plan to try some the newer models they have out now from Tru-Ball or Carter that are superior to the older styles.