>>150100811
You have 4 tries to get 10 yards. If you don't get the 10 yards the other team gets the ball, and can also get the ball if the other team obtains possession through an interception of a pass or a recovery of a fumble they get the ball.
Every play on offense is a designed play with each player doing something individually that makes up the entire play. Same on defense. It can get complex actually, even just the blocking schemes of the guys protecting the QB can be complex. Defenses too.