Think of an immense army composed of millions of soldiers. They are advancing toward a common target, they encounter obstacles on the way and find themselves in mortal danger, but in spite of all these difficulties the army does not give up. The space these soldiers must traverse in order to reach their target is one hundred thousand times larger than they are themselves. Of course, such a crowded army setting out on such a difficult road will need guides and equipment to help them reach their goal.
This huge army with 300 million soldiers is inside the male body. The soldiers are the sperm. Each one is about one hundredth of a millimetre in size. Their target is to reach the egg cell, and to do this, they must travel a very long road.
Of the 300 million sperm cells that set out on the road together, only the strongest one thousand will succeed in reaching the egg. Out of these only one single sperm will win the race and fertilise the egg. Before entering this race, the sperm first set out on a long journey within the male reproductive organs, passing through various stages on their way to maturity. In this maturing process, the sperm have many helpers.