their are 1000 ways of getting material. Hera are some for example:
go to youtube, find a video, copy the link to keepvid.com download the "high quality" mp4 video.
Install handbrake, rip a dvd you own, edit it.
search google for free stock footage video.
But you'll have to tell a story with your video. So you could also try to make photo's, add them to imovie, use the ken-burns effect and cut them and animate them so they tell a story.