3 stages of Chess
Opening: The opening is like in a baseball game when all of the players are warming up before the game starts, people slowly start coming in. Except in a chess game the game has started and the players (pieces) are taking their positions trying to gain positional advantages.
Middle Game: The middle game starts once the majority of the minor prices have be captured (knights, bishops, e.c.t). It is when you begin to worry about material advantages as well as positional.
End Game: It is unclear when the end game starts but it is when few pieces are still on the board and you are trying to win that wining point before the other team does.