You play X and the computer plays O. Take turns placing a mark on an empty square. The first to fill a whole line wins, and a line can go across, down or diagonally. Who goes first changes every round, and you get one hint per game. On the 3x3 board the Pro computer never loses, so a draw there means you played perfectly.
Explore every row, column and diagonal that can win through a square. A route containing both X and O is blocked.