Need help with a shy girl!!!!!! help me

OK here the thing, i notice this cute girl in school, but this the weird thing, i just have the urge to be friend with her so dont think that im a boy who goes around and pick on a cute girl and try to eff her, non of that. I try to talk to her once, she didnt answer me so that was kinda awkward. this what i know about her: she's a shy girl, not that many friends (just hang out with her sis and sis's friend), and she dont talk alot. Once i walked by her said a hello but she never answer back and kept walking. the second time i tried to talk to her, she was talking back and i just blank out of stuff to talk about, i really want to be friend with this girl so plz help me thx.