Two players, X and O, play a classic game of tic tac toe. Nine categories are displayed on the board. The champion, playing X, selects first. If they get their question right, their symbol goes into the box that category occupied. Also, money goes into the pot. For a question on the outer boxes, $100 and for a center box question, $200. Center box questions are tougher, and sometimes require more than one answer. If their answer is incorrect, nothing happens and their opponent selects.
After each has had a turn, the board shuffles and play moves to X again. Any black-colored categories now on the board are "jump-ins" and each player puts their hand over the buzzers. The first to buzz-in answers the question and a right answer earns the box. The first player to achieve "Tic Tac Dough" either across, up and down or diagonally wins the pot and the chance to go to the bonus. If a game ends where there is no "Tic Tac Dough" then a final jump-in is asked to determine a winner.
The game premise remained unchanged, but some little and some big changes were made to the game. Outer boxes were now worth $200, and the center $300. Games without a winner now were not decided via jump-in. The amount in the pot carried over to the next game for as many games neccesary to decide the match. The losing contestant is awarded $500 for every tie game, and the winner gets the entire pot.
Perhaps the biggest influence on the main game though was the addition of red categories in the early 80s. These especially increased in the final seasons where three such categories on the board was not uncommon. For descriptions of these special categories, click the link above.