I use this knot often because it looks nice, is functional, and easy to learn. This is just a short video showing how I learned to tie a lanyard knot with a loop. After tying, if the loop is the size you want, just work the slack out of the knot and tighten it up.
If you need the loop shorter, find one end of the loop lead and create some slack to work thru the knot as shown in the video. To make it longer, use one of the cords opposite the loop and work that slack towards the loop.
This knot goes by several names, here are a few more online links, that show up in a Google search, to help learn it from different perspectives:
Decorative knots #8
A simple lanyard knot
Boatswain's whistle knot
Lanyard loop knot