1 With yarn at front of work, insert right-hand needle from right to left through front of first stitch (st) on left-hand needle.
2 Wind yarn around right-hand needle. Pull yarn through stitch (st).
3 Slip original stitch (st) off needle. Repeat (rep) these steps until all stitches (sts) on left-hand needle have been transferred onto right-hand needle to complete one row of purling.
Courtesy of : Bernat