That just means when you finish the row and start that row you're confused about, you will look at each stitch and if it looks like it's a knit stitch, then knit it...and if it looks like a purl stitch, you purl it. Are you familiar with what the knit and purl stitch looks like? The knit stitch looks like a "v" and the purl has a little bump. Just take your time and you should be fine. Just don't forget to bring your yarn to the front for the purl stitch, then to the back for the knit stitch.