How do you write "castles" in algebraic? Sorry if this question is a duplicate one, but I can't find the algebraic notation for castling. What is it?
In either algebraic or descriptive notation, castling is notated 0-0 or O-O on the Kingside (when the King goes to g1 or g8) and 0-0-0 or O-O-O on the Queenside (when the King goes to c1 to c8).  See for example https://en.wikipedia.org/wiki/Algebraic_notation_(chess)#Castling