The playing of the game or the points standings?
Pretty much like it says: each team gets the ball on their opponents' 35-yard line, and can drive the football and attempt to score points. If after each team has had the ball one possession, the score is still tied, they do it again. If the score is still tied after that, the game is declared a tie and each team gets one point in the standings.
If a game is decided in overtime, the winner gets two points, and the loser gets none.