How to make a twisted cord
Measure a length of yarn 4 times longer than desired length of final twisted cord. Fold the strand in halfand make a slipknot at the cut ends. Pass the slipknot over a doorknob and stand far enough away so that the yarn hangs in midair and does not touch the ground.
Slip a crochet hook into the loop in your hand and, while still holding the yarn in the left hand, twirl the hook to twist the yarn around itself. Continue twisting until the yarn is quite taut and evenly twisted.
Still holding one end of the yarn in your left hand, with your right hand pinch the twisted strand midway between yourself and the doorknob. Bring the ends of the yarn together by moving toward the doorknob, but DO NOT LET GO OF THE MIDDLE OF THE TWISTED YARN. You will notice as you let go of the pinched midpoint of the twisted yarn it will twist around itself forming a plied cord.
Still holding tight to the ends so the twisted cord doesn't unwind itself, loose the yarn end from the doorknob and tie both ends together. You can run your finger between the cords to even out the twists if necessary.