Menstruation is also known by the terms menses, menstrual period, menstrual cycle or period 

Where

Now you would wonder that were does period happen so let me tell you all it flows from your uterus through your cervix and out of your body through your vagina

Why 

Now why does periods happens so periods happens for the baby in the womb so A egg travels through a thin tube it attaches to the wall of the uterus, where over time it develops into a baby.If the egg is not fertilized, the uterus lining breaks down and bleeds, causing a period.

When 

Now period happen even in the age of 10 and It normally happens every 24 to 28 day but It can range from day 24 to day 38 of your cycle.

Thank you 😊