How do you play the game tic-tac-toe?
1. The game is played on a grid that's 3 squares by 3 squares.
2. You are X, your friend 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.