There are two advantages provided by castling:
1. The King is safer near the corner behind a wall of pawns.
2. Brings the Rook towards the center where it can get into the action
more easily.
King and Rook move normally on subequent turns.
There is no such move as 'uncastle', but some people use this term to
describe a series of Rook and King moves that restore the position of Rook
and King before castling.