Lesson
White to move. Main line: 1. Kc5 Kd7 2. Kb6 Kc8 3. Ka7
Kc5 does more than approach the b-pawn: it occupies the route the black king wants to use. After ...Kd7, Kb6 keeps the kings separated while claiming the squares in front of the pawn.
By the time White reaches a7, the defending king has been pushed to c8 and can no longer establish a blockade on b8. White will support b5–b6–b7 and promote with the king shielding the pawn.
Shouldering is opposition with direction. Instead of facing the enemy king head-on, your king uses its zone of control to force the defender onto a longer path. Look for it whenever both kings are racing toward the same passed pawn.