To repeat the key introductory point: before thinking about what move to make, consider what points you currently attack in the enemy camp and whether any of the possibilities can be made profitable. Here White has two captures to consider: QxQ and BxN. What prevents QxQ from succeeding? The protection Black’s queen enjoys from his knight. So White eliminates the defender with BxN+. After Black replies b7xBc6, White takes Black’s queen for free. Notice the check White’s bishop gave when it captured the knight. The check is critical, as otherwise Black replies QxQ+, and then after his queen is retaken plays b7xBc6—a wash. Giving check with the capture denies Black the time to make mischief with the piece that has just been stripped of its guard.