To start a duel with another player right click on their character and select the 'duel with' option. The other player will be informed of your request, and to accept your duel they must click on your character and also select the "duel-with" option. Once both players are happy with the options which have been decided they should press the accept button. The duel will continue until a player retreats (if allowed), or until one player has died. If a player dies the items they agreed to risk will land on the ground for the winner to take, but they will retain all their other items.