The blood and tissue leaves the body because it's no longer needed.
It comes from the uterus, the organ inside a woman's body where a baby grows.
A fertilized egg attaches to that cushiony lining and begins growing into a baby.
But most of the time, the egg does not get fertilized, the lining is shed, and the girl or woman has her period. They're not the kind you buy in a carton at the store! Each of these ovaries holds thousands of eggs, which are tiny (each no bigger than the tip of a pin).
They might not want you to "go out" with anyone yet, even if you're not really going out anywhere.
These couples usually don't last long and that's perfectly OK.
The best advice is to go slowly because it's easy for kids to get their feelings hurt.
A girl's first period, called menarche (say: MEH-nar-kee), signals that she is growing up and her body is preparing so that she might have a baby someday.
A period is the 2 to 7 days that a girl or woman experiences menstrual flow — blood and tissue that leaves the body through the vagina.