American football rules

The object of the game is to score more points than the opponent during the alloted time. Points are scored when a team has control of the ball but can also be scored when they do not. The team with the ball (the offense) has 4 tries (downs) to advance at least 10 yards, and can score points once they reach or near the opposite end of the field, called the end zone. If the offense does not advance at least 10 yards during their 4 downs, the team without the ball (the defense) regains control of the ball (called turnover on downs).
On offense, points are scored by advancing the ball into the opponent's end zone for a touchdown (worth six points), or by kicking the ball from the playing field through the raised vertical posts (the goal posts) in the back of that end zone for a field goal (worth three points). After scoring a touchdown, the offense is given one additional attempt to score. These attempts are termed point after touchdown (PAT) and are used to score 1 or 2 points as follows:
The offense may attempt a field goal kick which is worth 1 point.
The offense may attempt to re-advance the ball into the opponent's end zone for a two-point conversion worth 2 points.
While on defense, the defense attempts to prevent the offense from advancing the ball and scoring. If an offensive player loses the ball during play (a fumble) or the ball is caught by a defensive player while still in the air (an interception), the defense may attempt to run into the offense's end zone for a touchdown. The defense may also score points by tackling the ball carrier in the offense's own end zone, called a safety (worth two points).