The game is 60 minutes long and is broken down into 4, 15 minutes quarters. If the game ends in a draw it will go into overtime witch means the first teams to score a touchdown.
A touch down is when an offensive player catches the ball that has been thrown to him in the end zone or a player is handed the ball and runs into the end zone. Or the defence can take it off the offence through a fumble or interception and they can then run into the others team end zone to score. A touchdown is awarded 6 points and then a kicker can kick the ball through the posts to gain them an extra point. Or they can go for two points and re put the ball in the end zone. You can also kick a field goal which is when the kicker kicks the ball through the posts at any stage of the game, much like an extra point after a touchdown but a field goal is worth 3 points. When a offenceive player gets tackled in their end zone it is called a safety and they are given 2 points.
Each team is made up of an 11 man offence and an 11 man defence and a 11 man group call special teams witch deal in kicking, punting and kick offs.
http://www.nfl.com/rulebook/lineup
