This screen holds the pads and the backing tracks for this device. Open it with Audio Tracks in Settings. Playing them during a song is on Pads and backing tracks.
Download Pads fetches the pad set. When they are on the device, the screen says Pads are loaded and shows the size. Delete Pads removes them.
Import Tracks adds audio files from this device. The list under that button shows each track and how many songs use it. Attach a track to a song by pressing and holding Play on the chart and choosing Play custom track.
Tracks shared across multiple songs or even across libraries are only stored once.