The first player is known as X and the second is O. Players alternate placing Xs and Os on the game board until either opponent has three in a row or all nine squares are filled. X always goes first.
The game is played on a grid that's 3 x 3. The first player to get 3 of their marks in a row (up, down, across, or diagonally) is the winner. When all 9 squares are full and no one has won, the game results within a tie.