Are any of Black’s pieces loose? Yes, the rook at a8; so that's our target. White’s queen has two ways to attack it: Qe4 and Qf3. Neither move yet inflicts a check, but perhaps the Black king can be drawn into position to be forked on f7 or h7 with an initial check or capture by another of White’s pieces. White plays Rxf7. If Black replies KxR, then Qf3+ wins the a8 rook. This is a good example of using a capture rather than a check to attract the king onto a square where it can be attacked; White forces the king to move by taking something that only it protects.