1) Step one: move the king first (to either side towards the rook) two squares.

2) Step two: jump the rook over the king, onto to the square directly beside the king.

Note the following requirements must be met in order to castle:

Castling can be done only if neither rook, nor king has been moved.

Also, one cannot castle to move out of "check", or through "check" (where an opponent's piece is attacking the king on the first rank), or if another piece is blocking the direct movement of the king and/or rook.

Castling may be performed on both "kingside and queenside" of the chessboard at any time during the game, provided the above conditions are met.

See: examples of castling.