Duels are where you have Player versus Player fights.
On the street you encounter regularly other wannabe stars who want to steal your thunder! Face them and knock them down a peg!
The winner of the fight gains glory and so climbs the ranking list. The loser loses some of their glory.
Each fight costs you 20 courage. If your courage bar is empty you need to wait until it has filled up. Alternatively you can fight immediately for a few diamonds or fill up your courage quickly!