You sound like you've never been to an eye exam before?
They will teach you how to put the contacts in, don't worry. First they need your prescription, so you'll have to read some letters off a wall. I don't know what else to tell you, it's pretty straightforward.
I am 13 too and I got contacts a few months ago. They will dilate your eyes and then do some basic tests to find your perscription. Then they will give you a pair of contacts and you just practice and learn how to put them in. And thats really it. haha. Good luck!! Have fun and contacts are great! it may take a few tries to get them on put dont give up or get too stressed out because you will get them in eventually.