GarageBand

Create a new GarageBand song with . . .

• Three tracks of loops
• at least 30 seconds in length

Then:

• Add two tracks that you play with the onscreen keyboard or musical typing

Then:

• Add a recording of someone's voice
• Apply effects so the voice sounds different
• Remove a part of the voice recording that you don't want by splitting the track or shortening a recording

Then:

• Fade out the song at the end using the Master Track (click here to see how to do that).
• Export the song to disk when you're done (Share-->Export Song to Disk).