You can add background music through this box. Also reorder and play them. Note, when you import the settings from another album with background music the MP3 files will not be imported (jAlbum can't do that), so you will have to add the MP3 files again to the new album.
Auto-start
With this option on the skin will try to auto-start the background music. Note, mobile platforms do not allow auto start by design - probably to spare with data. Also today even desktop browsers let the users decide if they want to allow auto starting media. So you can't force the background music to your visitors.
Controlled by slideshow
If the visitor starts the slideshow the music will start, and when pauses, it will pause too.
Loop
At the end of the music it will start over.
Retain play position
When the visitor changes directories (or refreshes the page) the music will continue where it was left off.