Fold the scarf in half width-wise so the two short edges line up. Give it a shake to get out any wrinkles.
Loop the folded scarf around the back of your neck so the fold hangs down one side and the loose tails hang down the other. Both sides should be approximately the same length.
Slide the end of the scarf with two loose tails through the loop on the other end of the scarf. Pull the tails, fitting the knot up under your chin.