Hey, the idea was that figuring out was also part of the experience as I spread clues here and there (both inside and outside the game).
The fact that you can not even do alt-f4 was also a mean to make you feel trapped within the game with no idea how to escape.
So spoiler :
To finish a level you have to make the smiles reach a square on the ground hidden in the level.
To make them move you have to attract them by activating one of the cross on the ground, it will always go to the closer one.