If the stitches on the left needle look like a V that's a knit stitch so you knit the row; if they have a bump on them, that's a purl and you purl the row. It's much easier to learn what the stitches look like so you don't have to write down each row. That's called 'reading your stitches' and it's useful to know when you get to more complicated patterns. This thread
might be of some help to you with the videos and pictures that show the knit and purl stitches.