1. You need two folded cords secured with a lark’s head knot, so you have four strings to work with.
2. Move working cord 1 over cords 2 and 3, heading right. Pass it under the working cord 4.
3. Move working cord 4 to the left, passing it under the two middle cords and over working cord 1. Pull on both working cords to tighten the knot, while holding the middle cords steady.
4. The two working cord have switched places. Move working cord 1 to the left, passing it over the middle cords and under working cord 4.
5. Move working cord 4 to the left, passing under the middle cords and over cord 1 on the right.
6. Tighten the square knot by pulling on the working cords, while holding the middle cords steady.