We're going to use GarageBand to record our voiceovers. The Way we're going to do it is with the Podcast creation tool. Even though actually turning our recording into a podcast--technically, an audio file linked both to a web page and to the iTunes Podcast Library -- is beyond the scope of this short workshop, it's the easiest free tool for sound editing on the Mac.
Here's a link to Apple's video on how to use the Podcast Tool in Garage Band.
Then at the end of the process, we're going to send our "podcast" to iTunes, and from there bring it into iMovie.