As seen in Simply Knitting
To make purl stitches, just reverse the action of plain knit stitches
 Step 1Holding the needle with all the stitches on in your left hand, and ensuring that your ball end yarn is at the front of your work, insert the right-hand needle through the front loop of your first stitch as shown. |
 Step 2Wind the yarn around the tip of the right-hand needle from right to left, in an anti-clockwise motion, constantly keeping a slight tension on the yarn. |
 Step 3Now slip the right-hand needle back through the stitch, ensuring that you 'catch' the yarn that you've already wound around the needle. This creates a stitch on your right-hand needle. |
 Step 4Pushing the point of the right-hand needle a little further through the stitch you've just created, pull the first stitch off the left-hand needle. That's your first purl stitch! Repeat points 1-4 across the row. |