The Role of Testosterone
The main male sex hormone is testosterone and this is made by the testicles, starting at puberty. Testosterone is produced by specialized cells in the testis called the Leydig cells. When stimulated by the LH signal from the pituitary; these Leydig cells release testosterone into the blood stream. LH is the luteinizing hormone — the same gonadotropin hormone found in women.

It should be noted that there are two separate compartments in the testis and that the Leydig cells are outside the spermatogenic tubules where the sperms are manufactured. This factor explains why there is no relation between virility (which depends upon testosterone production) and fertility (which depends upon sperm production).
Testosterone does more than just allow men to produce sperm. It also triggers the growth of facial hair; the deepening of men’s voices, and the development of a male physique—all the changes which turn boys into men. Testosterone is also important in creating a desire for sex—it increases libido!
In addition to the need for testosterone, the production and maturation of sperm in the seminiferous tubules of the testis also require the stimulus provided by FSH produced by the pituitary gland—and this FSH is identical to that found in women.

When a man and woman have sexual intercourse, the man places his erect penis inside the woman’s vagina. Here the penis releases millions of sperm when ejaculation occurs. Once the sperm have been deposited in the vagina, they have a long and arduous journey ahead of them, like salmon entering the mouth of a river to swim upstream in order to spawn. Some of the sperm swim straight up into the fallopian tubes through the cervix and uterus; and some of them swim so fast, that they have been found in the tubes in as little as a few minutes after ejaculation. Many sperm die in the acidic vaginal fluid; and some enter the alkaline cervical mucus and cervical crypts. They are stored here and can remain alive for as long as 48 to 72 hours. During this time, the sperms are released in small numbers and these continue to swim towards the fallopian tubes. (This is why you don’t need to have sex every day to get pregnant even though the egg remains alive for only 24 hours.) Sperm in the female reproductive tract swim using their own energy; generated as a result of the whiplike activity of their tail which propels them on. Of the millions of sperms released during an ejaculation, only a few hundred will survive to make the arduous trip up to the egg. Perhaps this is why so

1. Fertilization occurs when sperm and egg unite, generally between the 13th and 15th days of the menstrual cycle
2. Fertilized egg starts to move towards the womb
3. First division of the fertilized egg occurs 30 hours after the single cell splits into two new cells
4. Second division take place 20 hours after the first, giving four cells. Subsequent divisions produce 8, 16, 32, 64, 128 cells and so on
5. Ball of cells passes from the fallopian tube into womb about four or five days after fertilization

Hundreds of millions of sperms are introduced into the vagina during sexual intercourse. They pass through the mucus in the lower end of the uterus and swim up the cavity of the uterus and along the fallopian tubes
many millions of sperms are produced in the first place even though only one is needed to fertilize the egg—because the wastage is so prodigious.