Laser: S-curves and by the lee

My downwind sailing needs some serious work. I'd really appreciate any descriptions of both a) by the lee sailing and b) 's-curves' in as simple and clear terms as possible. I've had a look at the Rooster article, but remain somewhat confused. In particular, what angle should my boom be at when sailing by the lee? In some videos and graphics, the boom sail seems to be forward of the mast. Is that correct? Where should I be sitting when sailing by the lee? Too, I have read lots about the potential of 's-curves', but I can find little to describe what they are or how to effect them in practice. I've searched this and other forums, but can't find the necessary level of detail and clarity. Thanks in advance to the community!

Peter