Menstruation can be confusing, just like a lot of the other changes that come with puberty. Some girls can't wait to start their periods. Others may feel afraid or anxious. Many girls (and most guys!) don't have a complete understanding of a woman's reproductive system or what actually happens during the menstrual cycle. That can make the process seem even more mysterious.Girls usually start to go through puberty between the ages of 8 and 13. Their bodies and minds change in many ways. Hormones kick off changes like growth and breast development. About 2 to 2½ years after a girl's breasts begin to develop, she usually gets her first menstrual period.About 6 months or so before getting her first period, a girl might notice an increased amount of clear vaginal discharge. This discharge is common.