My most recent 'ible used a box knot to make a Pink Ribbon Key Chain
out of paracord. Here are the steps to the box knot.
Step 1: Step 1
Lay out two pieces of paracord, approx. the same length, in a cross pattern crossing at roughly the middle of both pieces.
Lay the horizontal one over top of the vertical one.
Now take the top end, and bring it down over the horizontal piece, and off to the side a bit.