Everything you need to know about NFL football.

Check out each NFL team's website. Sorted by division.

Games are played on a field that is 100 yards long + ten yards in each end zone (total yardage = 120 yards).

Games last 60 minutes (divided into 4 - 15 minute quarters). If the game is tied at the end of the game then one 15 minute overtime is played. First one to score wins.

There are five ways to score:
A touchdown = 6 points and is awarded when a team reaches the endzone.
A field goal = 3 points and is awarded when the ball is kicked through the goal posts.
A safety = 2 points and is awarded when a team tackles the other team in their own end zone.
An extra point = 1 point and is awarded after a when a team kicks the ball through the goal posts after scoring a touchdown.
A two point conversion = 2 points and is awarded when a team reaches its own end zone after scoring a touchdown.

Offense is the team that has the ball and is trying to reach the endzone.
Defense is the team trying to stop the offense.
Offense has four downs (tries) to make 10 yards or score. Everytime the offense reaches or goes beyond the ten yard mark, they are awarded a first down. They then get a new four downs.
Teams can elect to punt the ball at any time or attempt a field goal. Once the ball is punted or kicked the other team is awarded pocession.
Special teams are the squads that play when the ball is being kicked or punted.

11 players are on the field for each team at one time.

Offense:
The quarterback (QB)takes the snap (the ball is handed back to him) at the beginning of the play and either hands the ball off, pitches it to another player, runs with the ball or throws it (if he is not tackled first).
Center = Snaps the ball to the quarterback and then blocks the opposing team from getting to the player carrying the ball (the ball carrier).
2 Guards stand on each side of the center and block the opposing team.
2 tackles stand to the outside of each guard and block as well.
(The center, guards, and tackles are referred to collectively as the Offensive Line).
Tight End - Blocks and catches the ball.
Wide Receivers - Usually line up on the outsides and catch the ball. They also block on running plays and occasionally on passing plays.
Full Back lines up in the back field (behind the QB). He blocks, runs, or catches the ball.
Half Back lines up behind the QB. Can run, block, or pass.

Any player on the field, except the offensive line, is allowed to catch the ball. Any player can run with the ball.

Everyone likes to say that defense wins games. They're right but not completely. A team needs more than defense unless they're the '85 Bears or the Ravens of a few years ago.
Defense can certainly keep a team in a game but it usually can't win the game all alone. The offense must produce too.
The basic job of the defense it to stop the other team from scoring any points. To do this, the defense is made up of three basic positions: defensive line, linebackers, and defensive backs.
The defensive line usually get down in a 3 (one hand on the ground)or 4 (both hands on the ground) point stanse. They line up directly across from the offensive line. Their usual job is to try to sack the opposing QB on pass plays and to try to tackle the runner on running plays. Sometimes, their job is to try and clog things up so the runner has ni place to go and the linebackers can run up and make the tackle. The players on the end of the line are called defensive ends while the players on the inside of the line are called defensive tackles.
The linebackers line up behind and outside of the defensive lines. These guys are usually faster and smaller than defensive lineman but they're bigger and slower than defensive backs. They stop the run, cover opposing receivers, and sometimes rush the QB.
Defensive backs are the last line of defense. They cover the opossing receivers and provide run support when the other team runs the ball. Sometimes a defensive back will rush the QB - this is known as a blitz. Cornerbacks play on the "corner" and always cover. Safeties play behind everyone.
Usually defenses will play with 7 linemen and linebackers and 4 defensive backs. A "3-4" defense is when 3 linemen and 4 linebackers are used. A "4-3" is when 4 linemen and 3 linebackers are used. In passing situations, a defense may go to a "nickel" or "dime" defense. A "nickel" is when there are 5 defensive backs on the field. A "dime" is when there are six DBs on the field.
There are no set rules for how many of each defensive position must be on the field and the players may move wherever they want on the defensive side of the ball.