Shrink the box so the contained balls barely have any space to move. You shrink the box by chopping off parts. If you need to move the balls to one side you can tilt and shake your device.
This game trains your 3D spatial awareness, you can tilt your device to increase your understanding of where the balls are in 3D space, as their shadows will be cast differently. When the volume remaining is 15% or less, youve completed the level.