Lesson
White to move. Main line: 1. Nd7 Rfe8 2. Nxb8
The knight leaps into d7, hitting b8 and f8 simultaneously. Black can only save one rook — after 1...Rfe8 the other falls to 2.Nxb8, winning a full rook.
The forking square is the key idea: a knight on d7 (or e6, c6, …) can strike two undefended pieces on the same colour of square. Scan for two enemy pieces a knight’s-move apart and look for the outpost between them.