Look at the Advanced techniques page for a video on picking up sts. Pretend the leg opening is your L needle, take the R needle and insert it into a stitch on the edge (that's picking up), wrap the yarn and pull through (that's the knit part). Do this in about 2 out of every 3 stitches all the way around. Or since it gives you specific number, if you start at the botton of the opening, you need 16 sts by the time you get to the top of it, so just space the sts however they need to be for that rate of pick up.
sue- knitting heretic