Just like many other sports, the objective of football is to have a higher score when time runs out than your opponent. Your playing field is 100 yards long and 53 yards wide.
You have this entire space to move the ball.
HOW TO SCOREAs depressing as this sounds, the game is primarily played 10 yards at a time. The offense (team with the ball) has 4 downs, or tries, to get the ball another 10 yards. When they move the ball 10 yards within those 4 downs, they get 4 more tries to move it another 10! Move it enough times for 10 yards and your team gets a Touchdown! A touchdown is your ultimate goal for the offense in football and will earn you 6 points on the scoreboard.
Let me put it this way.
My fiancé (we will call him Mars!) took me on a first date and it was a disaster. Then out of no where he saved it at the end by holding my hand on the way to the car and was a complete gentleman. I decided to give him another try at a good date (aka- a second down). The second date (or down) was a winner and I felt we were moving forward in the relationship, but not enough so that I wanted him to be Facebook official. On the 3rd date (or down) he rocked it out with a trip to the lake. This is just like football, Mars moved the ball 10 yards and gets to try his luck 4 more times (This is when the jumbo-tron reads "FIRST DOWN MARS!! YELL LOUDER!!").
BTW... He of course eventually became Facebook official, and we will call this a TOUCHDOWN for Team Mars!On the other hand...
Let's say the defense (the team trying to get the ball back from the offense) is just doing a great job and the offense can't get anywhere but a few yards down the field with the ball after 3 attempts. On the 4th attempt they kick it away from the defense so they can get the defense as far down the field as possible. They do this because after the 4th down the defense becomes the offense and vise versa. Where ever the ball ends up after the 4th down is where the defense takes over as the new offense. The further the offense kicks it, the further the defense (now the new offense) will have to move the ball to get a touchdown.
I'll make it easier to understand. Let's pretend instead that after the first and second date, Mars then BLEW third date big time by taking me to McDonalds then asking me to pay because he is broke as a joke. 
What we then want to do is kick Mars as far away as possible so we never have to see him again. This is what the offense does to the defense!
What we then want to do is kick Mars as far away as possible so we never have to see him again. This is what the offense does to the defense!Play then resumes going the opposite direction and the strive for 10 yards at a time starts all over again.
Images Courtest of from top to bottom:
http://www.nflfootball101.com/
http://collegecandy.files.wordpress.com
http://mashable.com/
Drew Brees of the New Orleans Saints- Quarterback (and Super Bowl Champion!)
Miles Austin... a.k.a. "Mr. Kardashian"- Wide Receiver for the Dallas Cowboys
LOVE Peyton Manning! Quarterback for the Colts!
This stud muffin is Jake Locker- the Quarterback for the University of Washington and is in the top 5 players to watch for the 2010 season. 
Always secretly wished that I had chosen a school that was red and black! Easiest colors to put together
Another real cute dress from www.hautefancouture.com. They also have similar dresses any many different color so you can pick out your favorite team!
Also, think about the free pom poms you get with your team's colors at the games, potential 1.5 seconds of fame from your appearance on the jumbotron, amazing photo-ops to post to facebook and of course the after party to celebrate your teams win!