I have a piano question?

I am learning the piano, and the program I'm using only shows you how to play using the middle C position. I think I have that down but it only shows the notes on certain places on the staff, if that makes sense. I have a songbook full of songs I really want to learn on piano but the notes are on places on the staff that I haven't learned yet. For example: the G note is the highest note, which is on the second line. But there are notes in the book that are on the third or fourth lines. Sorry if that was confusing but I really need some help! Where do I play the notes on the keyboard that appear on those places on the staff?