The purpose of American football is to move the ball towards the opposition's end zone and ultimately into their end zone (a touchdown).
This is achieved by either running with the ball until tackled, or throwing the ball down field to a team mate.

Downs are the most fundamental part of NFL play. The offensive team moves the ball forward in sections of at least 10 yards. They have four chances (or downs) to gain those 10 yards. Each time the ball is advanced at least 10 yards within their four chances, another first down is earned, with four more chances to go a further 10 yards.
If the offensive team fails to move 10 yards within four downs, possession is surrendered. However, the ball is usually punted to the defending team on fourth down.

• There are 11 players from each team on field at any one time

• Four 15min quarters
• Three time-outs per half for each team
• 12min half-time
• 15min sudden-death overtime if scores are tied

•    A touchdown is worth six points, and is scored when a team crosses the opposition's goal line with the ball, or catches or collects the ball in the end zone.
•    A Field goal is worth three points. Field goals are usually attempted on fourth down if the kicker is close enough to the end zone to kick the ball through the posts.
•    An extra point is earned by kicking the ball through the uprights after a touchdown. The team can go for two points by taking the ball into the end zone again.
•    Two points is awarded to the defensive team for a safety when a member of the offensive team is tackled with the ball in his own end zone.

•    Backfield: The group of offensive players — the running backs and quarterback — who line up behind the line of scrimmage.
•    Down: A period of action that starts when the ball is put into play and ends when the ball is ruled dead (meaning the play is completed). The offense gets four downs to advance the ball 10 yards. If it fails to do so, it must surrender the ball to the opponent, usually by punting on the fourth down.
•    Drive: The series of plays when the offense has the football, until it punts or scores and the other team gets possession of the ball.
•    End zone: A 10-yard-long area at each end of the field. You score a touchdown when you enter the end zone in control of the football. If you’re tackled in your own end zone while in possession of the football, the other team gets a safety.
•    Extra point: A kick, worth one point, that’s typically attempted after every touchdown (it’s also known as the point after touchdown, or PAT). The ball is placed on either the 2-yard line (in the NFL) or the 3-yard line (in college and high school) and is generally kicked from inside the 10-yard line after being snapped to the holder. It must sail between the uprights and above the crossbar of the goalpost to be considered good.
•    Fair catch: When the player returning a punt waves his extended arm from side to side over his head. After signaling for a fair catch, a player can’t run with the ball, and those attempting to tackle him can’t touch him.
•    Field goal: A kick, worth three points, that can be attempted from anywhere on the field but is usually attempted within 40 yards of the goalpost. Like an extra point, a kick must sail above the crossbar and between the uprights of the goalpost to be ruled good.
•    Fumble: The act of losing possession of the ball while running with it or being tackled. Members of the offense and defense can recover a fumble. If the defense recovers the fumble, the fumble is called a turnover.
•    Handoff: The act of giving the ball to another player. Handoffs usually occur between the quarterback and a running back.
•    Hash marks: The lines on the center of the field that signify 1 yard on the field. Before every play, the ball is spotted between the hash marks or on the hash marks, depending on where the ball carrier was tackled on the preceding play.
•    Huddle: When the 11 players on the field come together to discuss strategy between plays. On offense, the quarterback relays the plays in the huddle.
•    Incompletion: A forward pass that falls to the ground because no receiver could catch it, or a pass that a receiver dropped or caught out of bounds.
•    Interception: A pass that’s caught by a defensive player, ending the offense’s possession of the ball.
•    Kickoff: A free kick (meaning the receiving team can’t make an attempt to block it) that puts the ball into play. A kickoff is used at the start of the first and third quarters and after every touchdown and successful field goal.
•    Line of scrimmage: An imaginary line that extends from where the football is placed at the end of a play to both sides of the field. Neither the offense nor the defense can cross the line until the football is put in play again.
•    Offensive line: The human wall of five men who block for and protect the quarterback and ball carriers. Every line has a center (who snaps the ball), two guards, and two

• Quarterbacks and kickers wear from 1 to 19.
• Running backs and defensive backs wear from 20 to 49.
• Linebackers wear from 50 to 59 or 90 to 99.
• Offensive linemen wear from 50 to 79.
• Defensive linemen wear from 60 to 79 or 90 to 99.
• Receivers wear from 10 to 19 or 80 to 89.