The purl stitch is not really different from the knit stitch, but is rather the inverse of the knit stitch.
The opposite side of any knit stitch is a purl stitch.
Step 2. Wrap the yarn around the tip of the right needle so that it moves under the tip of the needle.
Step 3. Pull the new purl stitch through the old one, creating a new purl stitch on the right needle. Slip the old purl off of the left needle.