Chess960, or Fischer Random, is a variant invented by the late World Champion Bobby Fischer. The rules of the game are the same as standard chess, but in an effort to reduce the impact of opening theory, the pieces have been randomly shuffled on each player's back rank.
Games end in the traditional ways of checkmate, stalemate and time-out.
Bishops must still be on opposite colors in the initial Chess960 position.
The king must be between the rooks to maintain the ability to castle both ways. That means a king can only be placed between the squares b1 and g1 or b8 and g8 for Black.
This means:
No matter the location of the king and rook, standard rules of castling apply. It must be the first move for both king and rook, the king may not travel into or through check, and there may be no pieces on any square that either piece travels through.
The king and rook end the process of castling where they would in a standard chess game. Example: Even if a white king is on b1 and a rook is on e1, castling kingside would involve dragging the white king to g1 (its final destination square), which will automatically move the white rook from e1 to f1, as White will always have the king on g1 and the rook on f1 in the final castled position. See here for more explanation about castling in 960
Fischer Random (Chess960) online chess game at Chess.com