This is very easy, it is the reverse, basically of the knit stitch. Insert right hook downwards into stitch on left kneedle. Loop the yarn around the needle and pull it out, (while keeping the loop on the needle) and up.
To make a Purl stitch is really quite simple. First you bring your yarn forward(In front of the needles instead of behind the work). The right needle goes in front of the left needle instead behind it. Lay the yarn over the stitch and make the stitch.
For righthanded: Hold the needle with stitches in left hand with the yarn in the front. With your right hand, insert an empty needle into the first stitch from right to left and wrap the free yarn once around the needle and pull through. Repeat across row.
When about to make the next stitch, place the working strand on the side of the work facing you. Then put the working needle into the front of the next stitch. Wrap the yarn around the working needle and flip the stitch onto the working needle as usual.