Tic-tac-toe (also known as XO) is a paper-and-pencil game for two players, X and O, who take turns marking the spaces in a 3×3 grid. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game.
By optimal play the first player is able to win or draw in each game. The game has only 13 possible opening positions 7 of which will make the first player win.
To have a good opening as O, remember these two important role.