How does a boy get a girl pregnant?

For a healthy adult male to get a healthy adult female pregnant. He must first have an erect penis, this must then be introduced into the vagina of the female. (if it is the first time that this has ever happened to the female then there may be some momentary resistance and discomfort and bleeding as the hymen is broken.) the penis is further stimulated by bringing it forward and backwards in the vagina until the male reaches orgasm and ejaculates. this releases sperm into the female and assuming that the timing is correct one of his sperm will meet her ovum the result of which will be a pregnancy. This is ridiculously simple explanation.