Lesson
White to move. Main line: 1. Bh3+ Kd5 2. Bxc8
1.Bh3+ checks along h3–e6. Black must move the king and has no tempo to rescue the queen on c8.
Once the king leaves e6, the same bishop continues down the diagonal with 2.Bxc8. That continuation along one line is the defining geometry of a skewer.
Pins put the valuable piece behind; skewers put it in front. Whenever king and queen share a rank, file or diagonal, look for a forcing line attack.
Bishops are the natural skewering piece because a diagonal crosses the board from corner to corner, and a king in the open is almost always sharing one with something. When the enemy king and queen are both loose, check the four diagonals first.