Oh! Okay, Sue got it. You just take a new skein of yarn and stick your needle under a loop (I use a single loop) and wrap the yarn and pull it through just like a reg knit stitch.
It can be a bit loose, but after a few rows and a tug on the tail it usually is fine. I do find that sometimes in the area between the pu stitches and the cast on stitches on waste yarn there can be a bit of a hole. What I do quite often is just pick up an extra stitch on either side of those pu stitches and continue knitting. Then knit two together on the next row at that spot. It doesn't show and is under the arm anyway. Cleans that right up!