The penis consists of 3 chambers of spongy tissue which absorb blood that reach the penis from the circulatory system. As these chambers fill with blood, it leads to the erection of the penis. When exercises are done continuously, in a right way, it will cause an expansion in the size of the chambers. Then, it will become able to absorb larger amounts of blood and this will lead to an increase in the size of the penis, and the purpose of these exercises is to create a tensile strength by stretching the tissues that are responsible for erection of the penis and this tensile strength will lead to an increase in the growth of those tissues, gradually. 
Another option for an “emergency” short term size increase is simply having a warm bath, a shower, wrapping your penis with a wet and warm towel or simply pulling it by hand. The blood flow increases and the flaccid size increases, too. The effect only lasts for minutes, but there are situations this may become handy, especially if you were in a cold environment before and your penis size has “shrunk” to even smaller than usual.
Professor Ralph at UCL believes that some clinics are feeding patients’ unrealistic expectations. “Initially, they don’t see doctors, they see sales people. It’s a hard sell: ‘We can get you an extra inch or two.’ I’ve been practising in the NHS for 30 years: if it was that easy to increase the length of a normal penis, I’d be in the Mediterranean on my cruise liner now.”

Unfortunately nobody can say how long it will take you. One individual may gain that in a few months while another may need 5 years to obtain it. Everyone is different, and genetics, routines, dedication, and many other factors come into play. Some people gain very easily while others have to “fight tooth and nail” for every 1/16 inch. I personally believe this has a lot to do with the thickness of the tunica albuginea, which is the thick, fibrous sheath covering the penile chambers (cavernosa). Think of it in this manner: the tunica is a bike tire, while the smooth muscle and cavernosa are the inner tube. The inner tube (erectile tissue) fills with air (blood) and expands until it fills the tire. If the tire (tunica) is thick it will be limited in how far it can expand. If the tire is thinner, it will be able to expand much further. Depending on how thick or thin your tunica is will have a bearing on how fast or easy you can gain. But to give you an idea, I can tell you that I am what one would consider a hard gainer. However with 2 years of PE and very consistent and dedicated work, I have gained a total of 5/8" length and 5/16-3/8" girth."

“Operations are very safe,” says Viel, who founded the London Centre for Aesthetic Surgery with his twin brother Maurizio. “Perhaps 95% of our patients are very happy. Where they are not, it is often to do with expectations. Some men want 10 inches when nature gave them four or five. I have to say, gently, ‘This is not possible. I am not a miracle worker.’”
...follow the program I outlined. If he smokes, he should quit. If he's sedentary, he should exercise regularly, ideally the equivalent of 30-60 minutes a day of brisk walking. To add a meditative, deep relaxation component, he might try yoga, or tai chi. And if he eats a lot of meat and cheese, he should try a few meat-less, cheese-less days a week, and eat more fruits and vegetables. This lifestyle approach won't change his size overnight, but over time (like a year), you might notice a difference.

Neither food nor any supplements influence penis growth or size. That’s the reason why all the so called penis pills offered on the internet simply don’t work at all, don’t believe all the fake promises. All those pills increase the blood flow only, which may cause a harder erections, but the effect instantly stops once you stop taking those pills. So, a lot of wasted money for non-permanent effect. It’s tempting, the sellers of those pills will show you doctors smiling from their websites, pseudo scientific studies from India they paid for, raving testimonials from famous pornstars but it’s just a huge scam scheme. It’s an extremely profitable business, selling cheap herbs for astronomical prices, combined with often shady long term recurring billing that’s hard to cancel. Bottom line: Penis pills are pure “snake oil” often made of cheap ingredients importet from China, overpriced and even potentially harmful for you health. Especially the contamination with heavy metals and carcinogenic colorings is a possible problem. Some sellers claim their products are manufactured in FDA approved laboratories, but this doesn’t mean the product itself is controlled by the FDA, like prescription drugs.
Those who do not like the idea of taking a tablet every day can take liquid supplements. Liquid supplements contain the same ingredients found in the tablets. Instead of taking a single capsule every day, you simply drink a small amount of the liquid. Nutritional supplements come in several flavors, including a traditional flavor and a citrus flavor. You can drink the male enhancement liquid straight from the bottle, but some men prefer mixing the liquid supplement with water or another drink. The liquid products have the same benefits as the tablets and capsules.