Lesson
White to move. Main line: 1. Qc4+ Kf8 2. Qxc7
Qc4+ is a double attack. The queen checks along the fourth-rank diagonal toward g8 and simultaneously attacks c7 vertically. Because one target is the king, Black must answer that threat first.
After ...Kf8, Qxc7 removes the undefended rook. No sacrifice or long combination is required: the tactic succeeds because the queen’s lines intersect on c4 and the checking tempo prevents the rook from moving.
Queen forks are easiest to find by starting with checks. For each safe checking square, trace every rank, file and diagonal from the queen’s destination; a second target on any of those lines may turn the check into a material win.