This knot is also known as #787 in 'The Ashley Book of Knots'(ABoK), the sailor's knife lanyard knot, marlinspike lanyard knot, single strand diamond knot, two strand diamond knot, and bosun's whistle knot.
I used and 18 inch length of paracord for the demonstration, which is more than needed, but this will work with various length/diameters of cord.
After the knot is tied, I also show the adjustment of the loop size by finding one of the loop leads and creating slack, which is worked back thru the knot. You can do it the other way around to make the loop longer.
This is just the way 'I' learned to tie this knot, there are other methods shown in books and online resources if you look for them.