As taken from wikipedia.
Jelqing is a technique intended to enlarge the penis by increasing the blood pressure in the penis, with the goal of permanently increasing the maximum erect size of the penis. This technique, also called "milking", involves wrapping the thumb and index finger around the penis while semi-erect and repeatedly drawing them away from one's body to force blood into the glans, thus encouraging more vascularity in the corpus cavernosa and associated tissues. Whether jelqing actually works or not is a subject of controversy.
The word (and technique) is rumored to have various Arabic origins (from the word "milking"); other sources claim the technique has its roots in tribal Africa (particularly Sudan); however, still other sources claim that it was an American invention and these rumors are simply rumors or propaganda meant to sell jelqing instructions. (According to wiktionary, entering جلق (jelq or jalgh) returns جلق زدن (jalgh zadan) meaning "to masturbate" in Persian. Persian and Arabic use the same basic script.) Still others maintain that this was ancient Russian tradition, practiced by midwives, and mothers for their sons early in life, as this was thought to enhance the size of the genitals. (Such techniques reportedly are the reason for Rasputin's massive organ) .Though there is a growing body of anecdotal evidence, and just one tiny non-blind study with very few participants that seem to suggest that it works, but otherwise there are no really definitive scientific studies to support the assertion or refute that this technique works, or that it is safe.
A study was performed in the late 1970s by Dr Brian Richards in the UK. It was published in the British Journal of Sexual Medicine and showed increases in 87 percent of the test subjects. Increases in penis length of up to 1.4 inches and girth of up to 1 inch were recorded.
Jelqing is inherently dangerous, and even if done correctly can cause injuries, from irritated skin and burst blood vessels to scarring and impaired penile function, including partial loss of erectile function and inability to maintain an erection. It should not be attempted by anyone without a complete understanding of the risks involved.
There are many products (tools, instructions, etc.) that one can buy; however, much of what they offer (instructions) is available on forums and free websites. Before beginning an enlargement regimen, one should contact someone experienced with the technique.
Jelqing is typically preceded by a warmup with a hot compress on the genitals, and concluded the same way.
Jelqing will often increase the size of the flaccid penis in the short-term after only a few sessions, but substantial gains to maximum erect penis size supposedly take a month or more to develop. Certain websites claim typically range in gains from .5 inches to 5 inches or more in length and .25 to 3 inches or more in girth. The upper end of the girth claims are highly suspect and the length claims represent many years of multiple enlargement techniques. However, there have been warnings that one possible cause of the growth is the presence of scar tissue caused by the exercise, which could conceivably harm penile function.
This technique is not recommended by the medical community.
With any person and any thing, it varies from person to person.