The squares can be revolved in the manner shown below. An angle can have four positions:
A square with a straight line can have two positions:
A square with a cross can't be rotated:
If you make a closed contour, for example, as complicated as this one:
then all the squares, whish constitute this contour will disappear and you'll get your points. The greater the number of squares in your contour and the higher the game speed, the greater will be your number of scores.
When the game speed increases, then new squares appear more often. The game ends when the field on the screen is filled up by the squares.
You can increase speed during the game by clicking "Speed".