Hey I have trouble talking to this girl I really like but schools out and I need to get her number some how?

The best way to try and get her attention is to write her a poem or a letter. Express to her how you feel about her. The only thing she can do is accept it or let you down easily. If you decide to do either one, just give her your number and wait and see if she calls you.

That’s simple, you need to put your game face on and not be nervous. but you need some practice, so this is your mission, tomorrow you greet everyone you walk past and ask every fifth person what time it is; AND YES THAT INCLUDES CHICKS. Unless of course you know for a fact that the person you are going to talk to is a douche bag.
While you’re doing this little exercise, you need to mix up your greetings and follow through with a smile or a smirk if you just said something slightly inappropriate. It is ok to be little nervous girls like that it makes them feel pretty.
Don’t look at your feet when you’re talking to a girl unless you have some witty comment about her shoes. BE CONFIDENT….
If you get denied don’t get upset and don’t get discouraged, right it off in your mind that she is gay and hit on some other hot girls.

No matter what you do you're always going to be nervous, also called "Approach Anxiety", when you approach women. It's something we all get. Best thing you can do is approach a dozen other women before the one you want to get the number from so you're already used to it and you don't think about it so much. Plus you may end up finding other women you are interested in during the process.