Lesson
White to move. Main line: 1. Nf6+ gxf6 2. Rxd8+
With 1.Nf6+ the knight gives check and steps off the d-file, unveiling the rook on d1 — which now stares straight down the file at the queen on d8. Black must deal with the check first, and after 1...gxf6 (or 1...Kh8) the queen has no escape from 2.Rxd8+.
This is the essence of a discovered attack: the piece that moves creates one threat (here, a check) while the piece behind it delivers another. When your own pieces line up behind the enemy queen or king, look for the front piece to move with tempo.