The PAT takes place on the 15 yard line (the one closer to the opposing team's end zone). It is an untimed scrimmage down, also called the try, where a team can kick the ball into the goal post for one point or run it into the end zone for two points.
If a team is unsuccessful, they earn zero additional points.
IMPORTANT: If you've ever wondered why a team only scored six points after a touchdown, it's because they missed the PAT.
The special teams will always perform the PAT.