You may want to add background music to your slider, to enhance the experience. This is very easy to do. Simply follow these steps:
This is the button with a 'gear' icon in it.
This will tell the slideshow to expect an audio file.
You can either add a url to an audiofile directly into the text box, or click on the '...' button to load a file browser. Navigate to the audiofile you want to play and add it to the slideshow. Ideally, audio files should be in an mp3 format.
After you click apply, the audio file will be added to the slideshow. Note that the sound does not play in the preview screen, so you will need to publish the slider in order to test the audio.