Please practice (and with your parents as listeners!) p. 17-18 in your book. Get comfortable with the open G string. Also, find the song, "London Bridge" and work on that too (page 18?-sorry left the book at home!)
For the refrain (that's a fancy word for the chorus part of a song), you can use this photo as a reference. I also included the chords of D and A if you just want to practice the rhythms of the song on open strings.