When it's 4th down, the team has to choose what to do...
- They can go for it and try to get the 1st down. The team runs a play to try to get the ball past the first down line. If they succeed, they get a new set of downs (4 more tries). The problem is that if they don't move the ball far enough (past the first down line), the other team gets the ball wherever they stop. So, this is a risky option - teams usually "go for it" when they don't have too far to go (like "4th and inches") or it is a close game and the game is almost over and they need to score.
- They can kick a field goal. Of course, this means they need to be close enough to the goalposts that their kicker can kick the ball between the posts at the end of the field (the goal posts). A field goal typically becomes a viable option when the team is about 30 yards from the endzone (the 0 line) or closer. If they make the field goal and the ball goes between the posts, they get 3 points. If they miss, the other team gets the ball wherever it was before they attempted the kick. (You will also see field goal attempts when there are only a few seconds left in the 2nd or 4th quarter, since if they miss, the other team won't get the ball.)
- They can punt the ball. This means that they kick the ball towards the endzone and the other team then gets to catch it, run it as far as they can, and take over on offense (and try to score themselves). This is choice you'll see most of the time, because it puts the other team further back than the other 2 choices.