Instructions
Check to make sure neither your king nor your rook has moved from their original positions at any point in the game. Castling cannot occur if either piece has moved at all. Keep this in mind as you start your chess game, and play accordingly.
Check to make sure there are no pieces standing between your king and your rook. If there are any pieces standing in any of those spots, castling cannot occur.
Determine whether any of your opponent's pieces can capture your king in its beginning position, its ending position or in any of the spots between the two. If your opponent can take out your king in any of these spots, castling cannot occur.
Move your rook over two spaces and your king to the space second from the end of the board. This is the move that is considered castling.
Use castling as an offensive move by putting your rook in a stronger position and keeping it from being captured by having your king right next to it.