Keep your brain in shape!
Fit all the 3D-puzzle pieces on the game board in such a way that it turns into a (flat) 2D-image.
One of the protruding sides of each puzzle piece has 1 ball, the other side has 2 balls.
So depending on how you orientate a puzzle piece, you get more or less balls.
When solved, all puzzle pieces will fit on the game board without any holes uncovered.