Hi Julian. This is how I would teach the SSC (my post from a different thread).
Other posters have explained what the SSC is, so I'll stick to how I would teach someone to use it. I would first teach the proper swing path, getting the up, across, and through components down and making sure the loop stays on the right side of the body. I wouldn't really mention anything about the use of specific joints unless the player were doing something egregiously wrong. Once my player has the correct swing, I will then start drilling him relentlessly with hand feeds, essentially forcing him to generate his own power. I will tell him to focus on keeping his arm relaxed and whippy and to generate a lot of racket speed. If I have done my job in teaching the swing path, he will not make errors, and he will get enough topspin to keep the ball in the court with a good margin for error. Nearly always, he will find the SSC on his own.
On most two handed backhands, the left arm is straight, and the right arm is bent in the contact zone. Does this answer your question?