The rook vs bishop ending is usually a draw. You can examine the drawing mechanism on the page about bishop vs rook.
There's an exception to this rule when the defending king is trapped in the wrong corner (the cornersquare covered by the bishop).
If you're white and you have the move in this position, your win will be easy.
If you attack the bishop with 1. Re7, then mate is unavoidable after 1...Bc5;
2. Re8+, Bf8;
And now after a waiting move like 3. Rd8 (or anywhere on the eighth rank) the king has to move to the corner and is mated after 3....Kh8; 4.Rxf8#.
Let's return to the initial position, but now black has the move.
This makes the position a little more difficult to win, but it's still a win.
The black bishop is only safe behind the king. There, the rook will not be able to combine the attack on the bishop with a mating threat.
So Black will defend with 1....Bg1;
Now you can win if you're able to flush the bishop out of its safe place behind the kings.
You can accomplish this by 2.Rf1 (attacking the bishop), Bh2 (staying behind the kings);
3. Rh1 (harassing the bishop again), Bg3 (still hoping to stay in the safe zone);
This forces the bishop out of the safe zone.
The bishop can't go to f2, because of the mating threat with Rc3 (or Ra3). If the king would then try to run away from this mate with Kf8, there's a double attack on rook and king with Rf3+.
And now, because you can combine the threats to the rook and the king, you'll win with
5.Rd3, Be7 (covering the d8 square);
Here 6. Rc3, decides the game.
Black has no way to save his bishop, Rc8 will follow.
If you find yourself in and endgame with rook vs bishop, you now have some useful ideas.
Trap the opponents king in the wrong corner and you'll be able to win.