Purling front and back is not something that you would do as a stitch for an entire project. This stitch sequence is usually meant to increase the total number of stitches in a row. Make sure that you have your project in front of you and that you are at the right location where you want to make the increases.
 Whenever you are purling, your working yarn needs to be in front of your project.Take a moment to bring the working yarn strand to the front of your work., To do the purl front part of the stitch sequence, insert your needle in and through the front of the loop. Then, yarn over the stitch and pull through. However, do not allow the old stitch to slide off of the needle as you create a new loop. Leave it where it is for now., To do the second part of the stitch sequence, insert the needle through the back of the loop, yarn over the needle, and pull through. This time allow the old loop to slide off the end of the needle as you create the new loop.This completes one purl front and back sequence.
 It is unlikely that your pattern only calls for a purl front and back stitch one time. You will likely have to do it multiple times in a row or over multiple rows to achieve the desired amount of increases. Look for purl front and back, or pfb, in your pattern and repeat the stitch sequence wherever it is indicated.
Start with a work in progress.
Bring the yarn to the front of your project.
Insert your needle through the front of the project and purl.
Insert through the back and purl again.
Repeat the sequence whenever pfb is indicated.
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