Find a quiet place to record your voice-over so that there's no background noise in your recording. Practice reading your script, or cue cards, a couple of times.
Press the "Record" button on your Flip Video and read your script or cue cards. The video footage you capture doesn't matter because you'll discard it later.
Upload the video file to your computer using the Flip Video's built-in USB connection.
Open the movie file in QuickTime Pro. Go to the "File" menu and select "Export."
Change the "Export" option to "Sound to AIFF" and change the "Use" drop-down menu to "Default Settings."
Combine the soundtrack you just created with video footage in your video editing software, and your voice-over is finished.