This video knitting tutorial will help you learn how to knit the purl front and back increase. This technique is similar to the knit front and back increase and is used on the purl side of stockinette, or to stay in pattern when increasing purled stitches.
NOTE: The example shown is done on the knit side (right side) of stockinette, but you would only do this for decorative reasons. It would normally be done on the purl side.
Also known as:P1FB
Step 1: With the yarn in front, purl the first stitch on your main needle.
Step 2: Before taking the stitch off the main needle, insert the tip of your working needle into the backside of the loop and purl it through the back loop. Then pull the stitch off the needle.
Example of the Purl One Front and Back Increase on Stockinette (PFB)