Here is a simple use of the two bishops to mate. Those are White’s only pieces, so work toward arranging them to mate one by one. First comes Be6, so that the light-squared bishop cuts off g8; now the king is highly vulnerable along the long dark diagonal. The move wasn’t a check, but since White now threatens mate with Bd4 Black’s reply is forced: he must protect the d4 square by playing Nb5 (his own bishop on c6 is not going to be any help because it runs on the light squares). This move does prevent mate via Bd4, but now White just directs his bishop to a different square on the same diagonal by playing Bh2 (preparing for Be5#). Black’s knight can’t defend e5 fast enough to stop the mate. Notice, of course, the crucial roles played by the pawns on the h-file. Without them, Black replies to White’s first move by evacuating his king to h7 or g7.