The other day, a Finnish lady on another forum gave a link to a Finnish website which has knitting videos. The video for purling is here:
You have to go to the bottom of the page and click on "Katso video!" in order to play the clip. The lady who does the video is speaking in Finnish, but it doesn't matter if you don't understand her. Just watch her video and watch what she does.
I knit continentally, and this is the way that I was was taught to purl (as in the Finnish video). You use the "pointer" finger of your right hand to direct the right needle and wind the yarn around the right needle tip before drawing the yarn back through the loop on the left needle.
Your left pointer finger stays stable and acts only as a guide for the yarn feed.
That webpage also has diagrams.
I hope it helps.