You have to arrange 8 pieces to a square. A single piece can be turned within its field by "+" and "-" and can be shifted by the arrow keys. After pressing of the space bar you can move the piece from its field to the field in the middle by "+" or move it back by "-". Now you can change the selected field by using the arrow keys. You can also use the mouse (click to select a field and "drag" to move or move back a piece).
If you are in mode "easy" then the position of the field is equal to the position of the piece in the square. If you are in mode "difficult" then the position may be exchanged in pairs (top-bottom, left-right).

Here you have to arrange the last two pieces, then the game is solved.