All About Your Period
Menstruation (your period) is the shedding of the uterine lining (endometrium). Overt menstruation (where there is bleeding from the uterus through the vagina) is found primarily in humans. Many women also notice shedding of the endometrium lining that appears as tissue mixed with the blood. An enzyme called plasmin — contained in the endometrium — tends to inhibit the blood from clotting. Periods last about 3-7 days. You usually get them aroung 8-17 but 12.5 is the average. Periods allow YOU to have children (in the future) if you chose. Your period can be up to 21-35 days long. Commonly periods last 28 days. But for the first 2 year they might be irregular because your hormones aren't balanced yet.
Diagram of The Female Reproductive System
This picture might seem disturbing but it helps (even though you think it doesn't.) This is the basic picture of inside you but you know it isn't actual inside you (sorry if it didn't make sense). It gives you the basics of what goes on inside you and what it looks like. If you want to find this go a little lower down then your belly button and draw a triangle going down toward your vayjay-jay.