A female is born with all the eggs she needs for her entire life already made and stored in 2 sack-like organs called ovaries. When a girl reaches puberty her ovaries release 1 egg per month. It leaves the body in a menstrual period unless it is fertilized by male sperm as a result of sex. Don't worry-eggs will not run out-a girl is born with 1-2 million eggs! Women stop releasing these eggs when they go through the menopause (age 40-50)-they are no longer fertile after this happens.
Attribution: Straight Talk Foundation