Unlike the en passant capture, this is a move in chess that I’ve known since I was a child. However, like the en passant capture, it has also caused me grief while playing against my iPod. I will explain why this move can be frustrating below in the “pro-tip.”
This is how to castle in chess: It is a move for your king and your rook at the same time, and it is a great way to develop your rook conservatively. This is a move that should be done early in the game.
It can only be done if neither the king nor the rook have been moved yet in the game. There can be no pieces on the board on the files between the king and the rook, and you cannot castle out of check. If you are doing a kingside castle, your king moves two files toward the rook, and the rook jumps over to the space just on the opposite side of where the king has moved to. A queenside castle is done exactly the same way (king moves two files toward the rook, rook jumps over king to the file immediately past him), but in the queenside case, the rook moves further.
Thanks again to Wikipedia, the abbreviations for queenside and kingside castling are O-O-O and O-O, respectively.
Pro-tip: If you are trying to castle while playing against a video game, computer or iPod, do not move your rook first and then try to move your king. The iPod will think that you are moving your rook in the normal sort of way that rooks move, and it will not think that you are trying to castle. What you need to do is move your king first, and then the computer will automatically realise that because a king can’t normally move two files, you are attempting to castle, and then it will automatically move your rook for you. Just trust me on this one.