When you work with 3 needles in a triangle, you are knitting 'in the round', like brendajos said. The thing that is different with knitting in the round is that EVERY row is like a right side row. You are almost always working only on the outside (the side that will be seen) of the item. So for that reason, stockinette stitch in the round is different than stockinette stitch knitted flat. When working in the round, knitting every stitch of every round will produce stockinette stitch. You will do no purling at all.
It would be helpful to place a stitch marker at the beginning of the round, just so you always know where it is for future directions.