If i were you i would have a little feel around just to get an idea of where it is so you dont just poke her anywhere and be gentle.Definatley dont rush as it will be hard for you to do it.The first time i did it we were both virgins both17 and he had no idea but neither did i.We had such a laugh when it finally happened as we tried a few times before that with nothing.It was about 2 months after we first tried before it penetrated.It was great because we were so comfortable with each other and were together about 6 mths sleeping in the same bed weekends nothing happened except u know just playing around but no sex.It might not happen first try so dont force it and wait till another time when you are both relaxed.