Begin with the tool oriented as pictured, with the center disc rotated up 90 degrees from the face of the tool.

Starting at corner A, place one end of line into the corner of the tool. Next, run the line through the slot in the disc closest to you and secure it in corner C. Repeat this step starting from corner D, placing the line in the slot furthest from you and securing it in corner B.

Rotate the disc at least four times away from you, making sure the lines remain in the slots. Once the four twists are complete, rotate an additional 1/4 turn.

Remove the tag end from corner D and thread it through the loop created when the disc was rotated. Next, remove the tag end from corner C and thread it through the loop on its side. 

Removed the loosely-wrapped knot from the tool. Pull the long ends (which were originally in corners A and B) away from each other until the knot begins to cinch on itself. As the knot closes, lubricate the lines (saliva or water works well) and complete the knot. Trim the tag ends as desired.