iTunes Music

You can use iTunes as a source of audio as well. Use it exactly the same as the CD, except you need to select "iTunes" in the Audio pane popup. If you have iTunes playlists, they will appear in the popup menu as well. You can use AIFF, MP3, or WAV files.

Click here to play the example. – MOV-File, 6.8 MB

Record your own audio
You need a microphone. Most are USB now, and cost about $50. Move the Playhead to the desired location. Click the record button in the Audio pane. Click stop to stop.