Make your parts first, putting each section in temporary elastics. When you're ready for the knots, take the elastics out and tie the knot by wrapping the hair around your fingers and pulling the hair through the loop. (Add an elastic to the end of the knot, otherwise it WILL come undone. Put the elastic as close to the knot as you can and surround it with hair to hide it.)
You can stop here if you want.
Or, add a few curls, why the heck "knot?" Yes, I'm a nerd, people!