Dear roadcomet, It may be hard to understand why something that can be inconvenient and even unpleasant is so important. The fact is that having your period, also called menstruation, is a sign that you re growing up. It means that your body is healthy and normal. Starting to menstruate is one of the changes that happen to girls when they begin puberty. The changes may begin when you re eight or they may not begin until you are in your mid-teens. Everyone is different and our bodies change at different rates and at different times. Here s how it works: Every month, tissue made up of blood vessels builds up inside the uterus to prepare for ovulation — when an egg is released from the ovary. Unless a sperm fertilizes the egg, and pregnancy happens, the egg breaks apart, and the lining of tissue and blood in the uterus isn t needed. It flows out of the uterus, through the cervix, into the vagina, and out of the body. This is called menstrual flow — it s having a period. Hope this information helps!