In American football, the team with the ball (offense) has 4 plays (downs) to advance at least 10 yards, and can score points once they reach the opposite end of the field, called end zone, or by kicking the ball through the goalposts. If the offense succeeds in advancing at least 10 yards, they earn a "first down" and the number of tries allotted is reset and then they are again given 4 tries to advance an additional 10 yards, starting from the spot to which they last advanced. If the offense does not advance at least 10 yards during their 4 downs, the team without the ball (defense) regains control of the ball.

On offense, points are scored by advancing the ball into the opponent's end zone for a touchdown (6 points), or by kicking the ball from the playing field through the goalposts (3 points). After scoring a touchdown, the offense is given an opportunity to score 1 extra point by kicking the field goal from 15 yards away, or 2 extra points by taking the ball into end zone from 2 yard line.

Defense can also score by causing a turnover by intercepting the pass or by picking up a dropped ball and taking the ball into the opponent's end zone for a touchdown. It can also score by forcing a SAFETY (2 points) by tackling the ball carrier from the offense in their own end zone. If the offense commits a foul while in its own end zone, that also results in a safety.

More Info: operations.nfl.com