The 2-Umpire System is the foundation from which 3-Umpire, 4-Umpire and 6-Umpire mechanics are built upon. It is crucial that you understand 2-Umpire mechanics before you can move up to 3-Umpire mechanics, since you revert to 2-Umpire mechanics when an umpire goes out to cover a trouble ball.
There are also three (3) situations where the PLATE UMPIRE must cover 3RD base, and one (1) situation where the PLATE UMPIRE must cover all bases. The 2-Umpire System must be learned thoroughly and is fundamental to your moving up.