The music and sound effects can be turned off through the Settings menu. To access them, tap the Settings button at the bottom left (it looks like a gear).

You will see three buttons corresponding to music, sound effects, and notifications. To disable them, simply tap the desired button and a red line will appear through the button indicating that it has been disabled.

These settings do not affect the volume used when ads are displayed. For that, you need to adjust the volume on your device.