The easiest way to learn how to use MovieMaker is to have something to do and to learn as you go. However it is quite useful to have an idea of what some of the buttons do before you start.
This tutorial is a good starting point but knowing what you want to do and finding out within MovieMaker is the best way to learn.
You will have to put a soundtrack on your movie. Using copy written music is illegal so here is a source of CC free music which you can download and use http://ccmixter.org/view/media/home.