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
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.