What's the pattern- is it open in the front or not? We can help you better if you're more specific. If it's open and you work back and forth on the circs, you knit just like on straight needles. At the underarms you separate the sts and work the back and fronts separately and the shaping is given in the pattern. If you knit in the round, work in the round to the underarms then separate the back and front and work the shaping for each section.
sue- knitting heretic