French knots are a knot type of stitch that have so many uses in embroidery. They can be single knots like eyes or used as a fill stitch that adds a lovely texture.
Bring up the needle. Then wrap the thread around the needle one or two times. The photo shows a knot with two wraps. The difference will be how large the knots are. If you want a smaller knot, use only one wrap. Either way is fine.
Hold firmly on the thread as you push the needle into the back of the fabric. I usually bring the needle down very near to where the needle came up. If you put it down in the same whole, there is a risk that the knot will pull through.