Congratulations on getting your period. Well, the first thing you should is to take a shower. Then, you need to look for either a pad or a tampon and put it on. You should also tell your mum because she can give you advice. Check out http://www.ubykotex.com.au/menstruation/first-period/ for more information.
menstrual periods are physiologically normal, no worries. however, if ever you use tampons, do change frequently because of the danger of toxic shock syndrome if you don't. you can google or do a wiki search on tss for more info.
The most important thing is to tell you mom. This is a big step as a teen or tween, and she'll want to know. Then she can help you find what pad is best for you, how to wash out bloodstains in undies, or on your bed (if that happened), and just help you through it.
Congratulations, indeed! Today, you are become a woman! It is an awesome thing, though it can also be a bit scary. After taking care of the physical requirements of applying a pad or inserting a tampon, do go talk to your Mom, or a trusted adult. If you have questions regarding what has happened, and will continue to happen regularly for quite a while, now, this is the time to ask them. Welcome to womanhood!