We return to the idea of cue-bids as an aid to bidding slams. Later you may see that cue-bids may be used in more prosaic ways for locating the best game contracts but here we are still bitten by the slam bug.
The principle is that when a trump suit has been agreed a bid in a new suit is a cue-bid, showing control of that suit and inviting partner to participate in a slam hunt.
As such, your hand has got to be of sufficient strength to justify the action; there is little point in making a cue-bid just to see the wheels go round. You have to be genuinely interested in better things.