Single mother in need of explanation

[Dumb_Blonde]

Thank you in advance for your time. I found a neat project to do with
my 14 year old son, but would like to know the science behind it so it
will be educational.

Here is the video link.

http://www.metacafe.com/watch/470767/firecracker_rocket_project_experiment/

It is a fire cracker experiment, and I know he will love it, but I am
clueless as to how this makes my car run