Increasing the volume of your ejaculate will directly affect the following aspects of your sexuality:

Increase the strength of your orgasms:
When you take such herbal supplements as amino acids or other natural sexual aids, your body can produce more ejaculate fluid, which increases the strength of your orgasms. Also, strengthening your pc muscle can greatly increase the force with which the ejaculate leaves your penis, making orgasms very intense.

Having a larger amount of ejaculate pass through the penis during an orgasm can prolong coitus (orgasm experience). The pumping sensation of an orgasm, of the semen and ejaculate fluids being pushed out through the ejaculatory ducts.
Improve your sperm count, and overall virility:

In order to fertilize an egg a large amount of sperm is required, many hundreds of millions. While the average man can produce this many sperm multiples times per day, there are external factors that can adversely affect the sperm count. Things such as smoking, drug use, poor diet, lack of exercise, and even wearing tight clothing in the groin area can all decrease the sperm count.
Increasing the volume of your sperm increases your fertility by increasing the number of sperm that are produced during each ejaculation. If you are trying to have children, the number of sperm you ejaculate is quite important, as is their condition. The pc exercise and amino acids such as L-Arginine and L-Lysine also help the health of your sperm, which increases your fertility and the chances of pregnancy (should you be seeking it).

Help your partner enjoy sex more:
When you ejaculate, your penis pumps semen and ejaculate, which many men and women find pleasurable. When you increase the amount of your ejaculate the pleasurable pumping feeling lasts longer, and also increases your pleasure. During intercourse extended pumping and orgasm pleasure improves the experience for both partners.

How do I do it?
Increasing the volume of your semen is done mainly through two things, taking herbal supplements such as amino acids, and the pc exercise.