In this position, White has to use Zugzwang to win. Zugzwang is often used in endgames to break down a fortress.
In this week’s problem. Black has constructed a fortress. There is no way through for the White King. But White can still win, provided he finds a way to use Zugzwang.
The solution to last Monday’s problem was that White plays 1 c5. He can then always block the Queenside pawns in such a way that Black has to move. Black then has to either move his King allowing White to play Kg6 and win, or move his f-pawn allowing White to play Kf5 and win.