Manual stretching exercises involve using your hand to massage the tissues along the length of your penis. This is intended to stretch the skin.
Jelqing is a penis stretching exercise. It involves massaging your penis tissues, stretching the skin to create "micro-tears" that look engorged.
Your penis isn't made of muscle, mostly its made of something like sponge. Regardless, no exercises or massages will make your penis larger. No oil, herb, food.