It is your job to create 3x3 square of dots before the computer can block you. In the top right is shown a set of dots, with a grey dot indication where your mouse pointer will be. Hit the space bar to rotate it into the direction you need it, and then click to place it. With each placement there will be a lightly colored X. That is where the computer is moving, and will be completely blocked off the board if you do not cover it immediately. After you make a 3x3 set it will clear those dots off the board giving you more room to work with. Each level you are given a certain number of sets, try to fill it all without letting the computer block you off and win.