It's a little hard to say without seeing exactly what the directions are telling you to do. If you can type out the first 3-4 sentences, we can be more exact.
It is possible that you are knitting the front and back separate, even though you are using circular needles. If they tell you to..."cast on 90 (or whatever) stitches...." then have you knitting rows, you'll be doing the front/back as separate pieces, using the circluar needles as if they were 2 straight needles.
If the directions say something like...." cast on 185 stitches and join in a circle...." then you would be knitting the front and back at the same time, in a circle or tube. when you get to the armholes, you will switch to back and forth, doing the front first, then the back.