To start a duel keep your weapon lowered until given the signal to attack. Do so by moving the mouse inside the safe zone.
When the time comes you can aim your gun using the mouse and shoot with the left mouse button. To win, simply kill the opponent before they kill you.
You only have six bullets so make each one count.
Shots to the leaves or stalk ( if the opponent has any) don't hurt.
Shots to the upper body cause heavy damage.
Clock shots are instant kills.
Shots to the lower body do the least amount of damage.