I refuse to apologize for All Knitting All the Time. Well, ok. But only a little.
1. Insert Stick. Yarn in front of work.
2. Bring yarn under and around the stick, back to front.
3. Push yarn through stitch on left stick. Much the same way you do a knit stitch. Only you're pushing instead of pulling through.
4. Pull the stitch off the left stick. That's a purl!