Also, when you are working on Rows 2 & 4, you are supposed to Purl all the stitches for those rows. (even the yo's from the rows before). Each yo from the previous row "counts" as a new stitch that you will purl.
So, it goes like this:
Row 1 - Do the stitches it says to
Row 2 - Purl all the stitches on this row
Row 3 - Do whatever it says
Row 4 - Purl all these stitches
The "ws" means that row is the "wrong side" of the scarf.