Say for example, you had a video that you made and it's lingering in some folder somewhere. You open up iDVD, find a template and then what? Now, you can use the "Import" command from the File menu, but there's an even easier way to do it.
Now, say your video's file name is "myRadVideo.mov"
It's as simple as dragging the video from its folder into the iDVD theme. Now, here's the tricky part. Most of the iDVD themes have "Drop Zones" on them, delineated by a black and yellow caution-style border. DO NOT put the video there. That will simply make it part of the theme. Instead, drag and drop the file somewhere else on the theme. You'll know you've done it right when the file name appears on the screen.
One last thing to do. Select that file name and type the word "Play." This will appear on the screen when the DVD is played as a clickable button. You can leave the original file name, but DVD convention dictates that people are looking for that "Play" button and not some odd file name. Don't want to give your professor any reason to not be able to watch your video.