First, try using the volume switch on the side of the device to adjust the sound level. If the volume switch is not on mute, make sure the volume is not set too low. For an iPad with iOS 6.0 or earlier, double tap the home screen. Make sure the volume control is not set on mute.
If your app is making sounds, but there's no music, you might have music turned off. To turn the music back on, open a profile, then click on the user's name at the top of the screen to access the "My Info" page. From here, you can toggle the background music on or off.