Help with kissing... I don't know what to do.?

Hey! I'm having an issue with kissing a girl. I have a girlfriend we are both 14 and we have been dating for 2.5 months and we both agree it's time to kiss. I have never kissed a girl before so i am clueless she has kissed a couple guys. I asked her "how do you initiate the kiss" she said "it just happens". I don't know what that means. Then she said just go with the flow. So how do you get it started? Should we discuss what kind it will be and how long?