Lesson
White to move. Main line: 1. Nf7+ Kg8 2. Nxd8
From f7 the knight checks the king on h8 and simultaneously attacks the queen on d8. The king cannot capture the knight and a knight check cannot be blocked, so after 1...Kg8 the queen falls to 2.Nxd8.
When a knight lands on a square attacking both the enemy king and queen, it is called a royal fork. The tell-tale pattern: a king in the corner and a queen a knight’s-move away, with a safe outpost like f7 or c7 in reach.