Tic Tac Toe is played on a 3 x 3 grid. You are X and your opponent is O. Players take turn putting their mark in empty squares. The first player to get 3 of their marks in a row (up, down, across, or diagonally) wins the game. 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.