There’s a defense and an offense. The ref flips the coin and the visiting team gets to pick heads or tails first. IF one of the teams picks heads and it lands on tails then the other team gets to either kick or receive.
When you are on offense everyone gets in their position, the Quarterback yells “HIKE” and the center gives the ball to the Quarter back through his legs. The quarterback throws the ball to someone who's open or if it’s a run play hands it to the halfback.
If you’re on defense you just have to tackle the offense. The main goal is to tackle the Quarterback; if you tackle him it’s called a sack.
The Quarterback is the main position of the team because there the people who make the plays and throws the ball. The center hands the ball to the Quarterback. There’s also wide receiver, cornerback, punter, kicker Etc.