Car crash please help!!!?

ok i was driving and i went to change lanes and the car in the other lane sped up and we like side swiped. the person from the other car just got out and looked at her car and then went back in her car. i just stayed in my car. we just drove away after that. i wanted to like go out and say something but like i didn't know what to do. i forgot to write down her license plate to. what will happen? please help!! i live in New York by the way