White has three checks to analyze: Qe7, Qf8, and Bxe6. The two queen checks, in response to either of which Black plays KxQ, almost create opportunities for White’s knight to fork the king and queen, but not quite; the forking square (e6) is protected in either case. So consider Bxe6+. Black's likely reply is BxB (we will consider an alternative in a moment). Now ask what checks you then would have, and you are returned to the same two queen checks mentioned a moment ago. Qf8+ requires KxQ (notice that the king can’t move to g6), leaving the Black king and queen on dark squares along with White’s knight. The forking square (e6) no longer is protected by the bishop; now the bishop is on e6. So 1. NxB+ works for White, netting a pawn. Notice the repeating pattern in the thought process involved: find a check; consider the response; look for another check, all the while keeping the changes occurring on the board clear in your mind’s eye and watching out for forks.
After White's initial Bxe6, Black has another option: Ke8. But now he immediately loses another pawn to Nxd5, with more complications to follow; so BxB is less costly.