This is more for newbies but I think we all could learn more about our penis.
For starters we need a good understanding of how the penis is constructed, and how it works. The penis is composed of three chambers; the two cavernous bodies (or corpora cavernosa) which lie side by side on the top of the penis, and the spongy body (or corpus spongiosum) which is centered below the other two. The spongy body surrounds the urethra, and extends out the end of the shaft to form the glans. All three chambers contain small hollow areas that can fill with blood to produce an erection. Surrounding all three bodies is a semi-elastic membrane called the tunica albuginea. The arteries that feed blood to the penis are surrounded by smooth muscle fibers that normally limit blood flow to the penis. When a man is aroused by thought, sight, or physical stimulation, the muscle fiber relaxes and blood flow into the penis increases. The spongy tissue of the penis fills with blood, causing the penis to swell. The size of the erect penis is governed by the tunica albuginea membrane, just as a bicycle tire limits the expansion of the inner tube inside it. As with a bike tire, once the limit of the membrane is reached, further pressure results in firmness rather than expansion. The veins that drain the penis lie close to the surface, and are compressed by the erection, thus slowing flow of blood from the penis.
Stretching the tunica albuginea has not been medically proven to change the errect length of the penis but as you will read, it is possible. Different methods work for different people so don’t get frustrated but instead get motivated. I would advice everyone to read all they can from any number of online sources of human anatomy before just jumping into this.