Opening / Middle Game / End Game?

The way I learned to define it was this:

The opening is the stage of the game in which players develop their pieces, get their king to safety, and attempt to control the center.

It switches to the middle game when players begin to attack each other, and defend.

The end game is when most of the pieces are off of the board. There is no definite number of pieces, but it's usually a safe bet to call it the endgame when each player has three pieces (knights, bishops, rooks, queens) or less.

Hope this helps! thanks 

The opening ends when you have completed the Opening Principles:

Opening: yes goood advise. but dont move queen early

Follow the Opening principles:

1.      Control the center squares – d4-e4-d5-e5

2.      Develop your minor pieces toward the center – piece activity is the key

Ø  Complete your development before moving a piece twice or starting an attack.

Ø  Move pieces not pawns.

3.      Castle

4.      Connect your rooks

Ø    By move 12, you should have connected your Rooks, or be about to do so.

 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.

Hope this helped! If you want more information Wikipedia has a few articles on it as well.