Italian Style of cuebidding involves showing either first or second round control in a suit below game. People who enter a cuebidding sequence often realize there is not the room to cuebid first round control and then at the next chance to bid the same suit again to cuebid second round control, so instead they will cuebid a second round control about which partner needs to hear.
The bidding: South could very well open the bidding with Two Clubs. At most he can lose one Spade, one Heart and two Clubs. Strictly speaking, he does not have 8.5 quick tricks, 22-plus high card points or game in his own hand so he opens One Spade.
North has 11 points in support of Spades and four-card support, so he immediately gives partner a limit raise. If he had only three Spades, he would normally bid a new suit at the two-level then bid Three Spades.
South knows they are in the slam ballpark and cuebids his Diamond controls. He skips Clubs because he does not have first or second round control in Clubs. North cuebids his second round Heart control but this bid has a hidden implication.
North knows South does not have first or second round Club control. If he did not have a Club control himself, he would know that slam is not possible. North, by continuing the cuebidding sequence promises a Club control.
South asks for keycards (aces and the King of trump) and bids Six Spades. South can use Blackwood with a worthless doubleton because his partner has already promised a club control.
The Lead: The King of Clubs is the natural lead being top of a solid suit.
The play: Declarer ruffs the second round of Clubs, draws one round of trump and claims.
Result: Six Spades is cold for +1430.