Basic rules of chess

Chess is more straightforward than people realize. Two sides, white and black, try to checkmate each other. Play starts with the white player and the players take turns moving one piece at a time until the game ends. The only exception is castling; when a player can move two pieces in one turn.

A player wins when either the opponent concedes or the enemy king is checkmated. Checkmate is when the enemy king is in check and the king cannot escape. The king can escape check by moving to a square not controlled by an enemy piece, by capturing the checking piece, or by blocking the check with a friendly piece. It is important to note that it is illegal for the king to move into check.

The game can end in a draw several different ways, but the two most common ways are for the players to either decide that neither side can win and agree to a draw or for the game to end in stalemate. Stalemate is when one side cannot make any legal moves.

Some of the weird rules:
Castling: This is the only time when two pieces can move in a single turn. Castling is done with the king and rook, and is used to evacuate the king from the center. The king can castle with either rook. To castle, the king moves two squares in the direction he wishes to castle, and the rook is placed on the other side. Now there are a few important restrictions. There can't be any pieces between the king and rook. Additionally, neither the king nor rook can have moved previously. And finally, the king cannot castle through check.

Pawn Promotion: When a pawn reaches the other side of the board, it can "promote" and become any other piece. Players generally promote to the best piece, the queen. Polygamy is allowed. I don't understand how all of this fits into the chess as war metaphor, but it's a good thing when you can promote your pawns.

En Passant: Meaning "in passing," en passant is used when you have a pawn on the fifth rank and an enemy pawn tries to move two squares past your pawn. Using en passant you are actually allowed to capture the cowardly pawn.