Start with four cords (or two doubled cords).
I have used different colors to make it easier for you to follow.
The two inside (yellow) cords are your "core" cords and will remain stationary as you make your knot.
The outside cords (orange and brown) are your knotting cords.
Place the right hand (brown) cord over the two core (yellow) cords.
Place it under the left hand (orange) cord.
Bring the left hand (orange) cord under the two core cords and up through the loop formed by the core cord and the brown cord.
Tighten by pulling gently on the knotting cords