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.
Step 2: Step 2
Now bring the bottom end up over the horizontal piece, and off to the other side a bit.
Step 3: Step 3
Take the end on either side (for me it was the right because I'm right handed), and bring it over top of the first piece, and underneath the second, so that it's caught in that little loop.
Step 4: Step 4
And now we take the other side (left in this case), and cross it over the first one, and under the second, so that it's caught in the other little loop.
Step 5: Step 5
Slowly tighten your knot. Some people find that leaving your index finger of your non-dominant hand makes this easier, I find that it's easy if you just go slow pulling on each a little at a time.
Step 6: Step 6
Now you should have a little box. So pull the strand that's on the top, down to the bottom, keeping it on the same side of your square as it starts on.
Step 7: Step 7
And take the strand on the bottom, and bring it to the top, keeping it on it's side of your square.
Step 8: Step 8
Same with the sides. In this case I've started with the right side again, bringing it to the left, keeping it in line with the last turn.
Step 9: Step 9
And again with the left, bringing it to the right, keeping it in line.
Step 10: Step 10
And pull tight once again.
Step 11: Repeat
Now just start the whole process again with step one, only now instead of two pieces that are crossed, you have two layers of box knots. With this you can do a whole lot of different paracord projects. Have fun!