You need to take a length of paracord lets say for example 14 inches then find the center and fold it over. Now you have 7 inches in length.
Now just tie a diamond knot, square knot, overhand knot at the end. Now you have your loop and knot. Then just tie your paracord in whatever style use want around this 7 inch loop and knot.
Of course the starter piece or the loop and knot length depends on the wrist size and what knot will be used to make the knot at the end. So its best to maybe start with a 24 inch piece of paracord then once folded over and knot applied you should have 6-8 depending on the knot used.