How to get closer to a girl?

Hi, im James and am 16, and i reli like this girl called Georgie and shes a bit younger than me. Being nervous around girls, i dnt know how to act. How can a get closer to her and get to know her (well, ive got to know her better recently) and how to i go about makin her know subtly tht i like her and then how do i ask her out etc? thnku