I used the search thing and nothing came up so ill tell you now. its actually pretty simple. you click on the person you want to duel and you press /duel (make sure its a melee class). Now the person is on auto attack. You own him real quick and the auto attack is still on and he will attack you! this will make him flagged. so if you're high lvl you can do this to a low lvl and if they accept you can gank them! =) Enjoy