First thing, insert needle up through fabric and taking your thread to left, make a loop shape and insert needle in and out as shown.
This will allow you to make a small catch in the centre of the bottom of the loop.
Take the needle point up on the right and about a third of the way up the side of the stitch.
You then pull your thread through and rethread it back through the small catch stitch to the other side. Take your thread down under fabric in a slightly loose manner so that it makes a nice curved stitch under the top loop.