When you castle queenside , the king ends up on c1 for White or c8 for Black, and the rook ends up on d1 for White or d8 for Black.

In simple terms:

  • White queenside castle: king e1 → c1 , rook a1 → d1.
  • Black queenside castle: king e8 → c8 , rook a8 → d8.

The king always moves two squares toward the rook, and the rook jumps to the square just on the other side of the king.