Rook versus bishop is a draw if the defending king reaches the corner of the opposite colour to its bishop. There the king can never be checked into zugzwang because the bishop always has a safe interposition or tempo move.
A rook against a bishop is normally a draw, but the defender must know where to put the king. The rule: go to the corner whose colour the bishop does not control. Black's bishop runs on light squares, so the safe corner is h8 (dark), and that is where the king is.