How do you make a book trailer?

I'm making a book trailer for Prince and the Pauper for an English class using clips from other movies (If you have any movie suggestions, check out my other question. Any help would be much appreciated and I almost always pick Best Answers!) but I don't even know how to take clips from movies. I could use either a mac or pc so suggestions or walkthroughs for both would be amazing.Thanks so much for any help!