I did a dishcloth that called for this. In MY case, what was called for was picking up the "horizontal stitch" and knitting it as well. The "horizontal stitch" in this case was the bar that existed between two knit stitches (this was down from my current row of knitting). I just reached down with my needle, grabbed that "bar" pulled it up and knit it with my next knitted stitch.
Hmmm.. I read that and it is clear as mud. I'll try to take or find a pix to better explain.