You've been knitting the instep or the part of the bootie that covers the top of the foot probably on 8sts. Now you're to take a new end of yarn and go back to the beginning of the instep and pick up 13sts. These 13sts will be picked up at the side of the instep. Then you knit across the 8sts at the end and finally pick up 13sts down the other side of the instep, working toward the base of the instep on that side. When you knit these sts you'll be making the sides of the bootie.
is approximately what you're supposed to do for picking up along the side of the instep.