This photo shows that I have already started the row of double knots. The first step is to come up from underneath and taking your thread to the left, make a very small stitch.
You then insert the needle through the caught thread.
The next photo shows how your loop that you made should sit before you insert the needle back in to make the double knot.
Next you insert the needle under the straight line of the stitch and hook it over both the loop and the hanging thread and pull it through to make a lovely knot.
Once your knot is completed you go on working to your left until the desired number of knots is made.