I am a novice knitter and in the process of knitting (and felting) a tote. I am now trying to figure out the directions for the "tote base". I am knitting on circular needles. After knitting the main part of the bag I was instructed to purl 4 rows. Here's the part I don't understand: "Next round: pick up and knit together with the stitch on the left needle and the bar from the last knit round." What's a bar and how do I pick it up?