How to get the girl I like?

i need hlp. this girl im in love with has a bf. iv known her for 2 years now and i rlly like her. she keeps sayin how if she cld find a bf at our school she wld dump her current one. im just not sure if she wants me to ask or if she is just telling me becuz im her close friend. last night we kissed but shes the type thats rlly flirty so its hrd for me to know wat to do. and even if i ask her out iv never had a gf during the school year and i wldnt know wat to do. we hav the same lunch this semester but i dont know how i shld act around her. wld i act as i always do or wat? also we go to the mall almost every weekend. any hlp wld be greatly appreciated. im 15 and shes 17