You probably already know how to play Tic Tac Toe. It's a really simple game, right? That's what most people think. But if you really wrap your brain around it, you'll discover that Tic Tac Toe isn't quite as simple as you think!

Tic Tac Toe (along with a lot of other games) involves looking ahead and trying to figure out what the person playing against you might do next.

RULES FOR TIC-TAC-TOE

1. The game is played on a grid that's 3 squares by 3 squares.

2. You are X, your friend (or the computer in this case) is O. Players take turns putting their marks in empty squares.

3. The first player to get 3 of her marks in a row (up, down, across, or diagonally) is the winner.

4. When all 9 squares are full, the game is over. If no player has 3 marks in a row, the game ends in a tie.