Cast on just one stitch, so if you're starting with a slip knot just leave it at that. The first row you will knit that stitch but do not slide the original stitch off the left needle yet. Move your working yarn between your needles to the front of your work and purl the same stitch, still not slipping the original stitch off the left needle (so at this point you have one stitch on the left needle and two stitches on the right needle). Now, move your working yarn between your needles to the back of the work and knit that stitch one more time. Now you can slip the original stitch off your left needle and you will have three stitches on the right needle. Turn your work and start the next row instructions.