When a male chicken wants to mate with a hen, he will do a little dance around her. Usally hens are not interested and just walk off. If a rooster feels like he just has to mate with a stubborn hen, he will chase her down. If he is fast enough to catch her, he will grab on to some feathers just below her comb and climb on. When the male bird is threading the hen he will grip her back with his claws and her head with his beak. This behaviour continues typically only during the breeding season (spring and early summer).
Roosters do not have penises. They have a sperm glob on their vent and will try to put it on the vent of the hen. Sometimes it works sometimes it does not. If you want eggs for hatching, put a rooster with no more then 6 hens together. As a rule, the more aggressive the male birds are, the greater the chance that their fertility levels will be high.
The sperm live inside the female reproductive system and each time an ovulation occurs (every 24-26 hours in good egg producers) the egg can become fertile. This process continues and matings at 7 - 10 day intervals are necessary to maintain fertility. After fertilization occurs the egg albumen, shell membranes, and shell are added to complete the egg formation process. The chicken usually lays the egg about 24 hours after ovulation.