For school I had to build a paper rocket. Now I have to explain how it works? LINK?

For science class, I had to make this rocket a href="http://spaceplace.nasa.gov/pop-rocket/" rel="nofollow"http://spaceplace.nasa.gov/pop-rocket//a I made the rocket, now one of the questions is : ''Using this page, explain how your pop-rocket works. Keep in mind the four elements of flight.'' Please answer this question. Thanks :) Cheers!- Kayla R.