American football in 20 seconds: You have 4 opportunities to advance the ball a cumulative 10 yards, upon doing so, your 4 opportunities reset. Advance past the goal line = 6 points + opportunity for 1 additional. Fail to move 10 yards? Ball possession transfers to opponent. If it's 4th down (final opportunity) you can hedge -- punt the ball (transfer possession, but about 40 yards further away) or attempt a field goal (place kick through yellow uprights), which is worth 3 points.

Obviously there are nuances but that's 90% of it right there, in a lot less than 10 minutes.