Figure 2.2.2.3[White to move]

Look for unprotected Black pieces and you find the rook at g5. Look for checks White can give with his queen and you find two: Qd8 and Qxg7 (be careful not to overlook a check just because the needed square is occupied by an enemy piece). Qd8 is the winning move; it checks the king and also attacks, and wins, the rook.