By 2 to 3 inches longer, I meant that when hooked up and slack taken out of the FM cord, the bow string will be about 2 inches ahead of your extended string fingers. then when you hook the fingers on the string, you will have a small loop in the FM cord. That allows enough room to make a release and then as Dave points out, you should just feel a "thump" in your bones. IF your elbow gets pulled forward you don't have your alignment correct.
The string hand needs to be as relaxed as possible to get the best release. The fingers are relaxed enough that the bow string flips them out of the way, you DO NOT open the fingers, the string does the job. The plate you see Rod using is to help remind you of the hand position, IF you cup the hand (use too much hand tension) the rear point of that tab plate will poke you and feel very uncomfortable. That's why it is there.
The bow sling is to help you relax the bow hand without fear of dropping the bow when you shoot.
IF!!!! you learn these two ideas using the "learning" devices, many can elect to not use them anymore, others will keep them as permanent pieces of equipment.
I see many that discard equipment devices because they "don't like them" or feel they interfere with their shot. And they well may. But that is the point! IF mastered, you will most likely be a better shot down the line. BUT!!! This isn't a "try it for a couple arrows" thing it IS a LONG term commitment to improve your shooting.
Arne