It usually needs two individuals which are different sexes from the same species. A man's sperm contains either an X or a Y chromosome.It works by combining genes from more than one source. When a sperm and ova combine to form a fertilised egg, the baby may get either of these chromosomes from its father.See instructions at Wiktionary: Entry layout#Translations.
For some species sex is not determined by inheritance, but instead by environmental factors experienced during development or later in life.
If the baby gets two X chromosomes, it will develop into a female.
If the baby gets one X and one Y, it will develop into a male.
Once it is in, a fast reaction goes through the egg cell wall to shut off all other sperm.
Sex determination in biology is about the function of sex, not what individuals look like.