I'm not sure why you asked this question under the category of pets and animals but I'm going to assume your question refers to a human being. :-)
The great thing about the school environment is you have (time) to gradually get to know someone. You start off by smiling and saying hello when your paths cross.
About a week or two later you might introduce yourself.
"I see you around all the time but I don't think we've officially met. My name is Mike (extend your hand while saying) and you are?"
Reference something you heard about at the school or ask her a question that is school related. After she answers tell her to have a good day.
If she is not in any of your classes make it a point (not to see her) for a few days or a week or so. The next time you see her greet her by name and ask her how things are going. Chat for a minute or two and tell her you have to get going; "Take care". Avoid her for another week.
The next time you "run into her" greet her by name and ask her (very casual like) if she has any lunch plans. If you feel nervous about it then tell her you're working on a project regarding dating and relationships. "Would you be willing to help me out by letting me interview you?" "Lunch is my treat." (smile)
Note: If you use the interview lie make sure you do some google searches or come up with a list of 25 -30 dating/relationship questions and bring them with you.
If she says yes you have an opportunity to ask her questions like "Are you currently seeing someone?" "Have you ever been in love?" "How do you know when someone loves you?" "What are your deal breakers?"....and so on.
(Remember to interject your sense of humor and see if there is any chemistry between you). If you hit it off tell her at the end of the interview (thank her ) and tell her that you'd like to take her out on a "real date" sometime if that's okay. If she says no to the interview or the date don't take it personal. At your age your should keep your options open and pursue multiple prospects!