You will be creating background music for your PowerPoint by humming a song in GarageBand; follow the directions below:
Open GarageBand and create a new voice file.
Save it as the following:
Then click on the red record button at the bottom and record yourself humming a song (or make up the song) while snapping your fingers for two minutes and when finished hit the red record button again to stop.
Next, on the right side, choose and apply the vocal effect of your choice.
Export the song to disk
Choose the MP3 file format and save to your Dropbox
In the first slide of your PowerPoint, go to Insert > Sound and Music > from File and select the mp3 music file you just made; choose to start it automatically. Apply the sound settings on the right and make sure the volume is set to low.