1. Depending on how long you want to square knot dictates the amount of thread you require. I will refer to this piece of thread as the ‘knotting thread’ from now on. (The pictures show a square knot finishing off a cord bracelet.)
 
2.  Take the left-hand strand of the knotting thread and make a loop over the top of the end strands by looping the end over towards the right.
 
3.  Pass the right strand of the knotting thread over the top of the left-hand knotting thread under the end strands, and up through the loop created by the left-end of the knotting thread.  Pull both ends of the knotting thread evenly to close the knot.
 
4.  Lay the right-hand strand of the knotting cord over the top of the end strands.
 
5.  Take the left-hand strand of the knotting cord and pass that over the top of the right-hand strand, under the end strands, and up through the loop created by the right knotting thread. 
Pull both ends of the knotting thread evenly to close the knot.
 
6.  Repeat left hand / right hand until you have completed all the knots needed.
 
7.  Trim off the excess and secure the knot with a small amount of glue where you trimmed off the excess.