The king can only move more than one square during a castling move. To castle, the king moves two square towards the rook, and rook moves to the other side of the king. This is all one move. You may only castle when :
All the squares between your king and rook are unoccupied.
The king has not moved yet
The rook involved in the castle has not moved yet
The king is not in check
The king will not move into check
The king will not move through a square being attacked
To castle when playing at Immortal Game just move the king. The rook will move automatically if the castle is valid AFTER the move is submitted.
Castling King Side
A King-side castling move may be made if neither the king nor the king-side rook has yet moved in the game and both squares between the king and the king-side rook are unoccupied.
Castling Queen Side
A Queen-side castling move may be made if neither the king nor the queen-side rook has yet moved in the game and all three squares between the king and the queen-side rook are unoccupied.