This is another way of saying "knit the knits and purl the purls". As you come to each stitch, you check to see if it appears to be a knit or a purl stitch and then work the stitch accordingly.
To do this, you need to be able to recognize your stitches. If the stitch appears to have a "vee" below the needle then it is a knit, and if it has a bump then it is a purl. There is someone here on KH (sorry, I can't remember who right now) who uses the analogy of a person wearing a scarf ... if it looks like the "scarf" is hanging around the person's neck then it is a knit, and if it looks like the "scarf" is wrapped around their neck like a noose then it is a purl.
One of the mods here has a great diagram that shows the difference between the knit and purl stitches ... if you're having trouble distinguishing them, I'm sure they'll be happy to post it for you!