It is very easy and looks a lot like a buttonhole stitch but much more defined.
Bring your thread up from back of work. Insert needle down and across as in the picture below.
As you can see in the next picture, you then go back to the left and insert needle in the same hole, but this time take you needle under and up on the diagonal to the right of the first stitch line.
As seen in the next picture, you have now made an 'L'shape stitch.
Repeat the above steps making another 'L'stitch.
Continue in the above manner until you have the required number of stitches. Finish the stitch off at the back of your work.