these, right? (It's OK to post the link.)
You've got those stitches on a stitch holder. These will be the stitches that are in the center of the front, between the 2 leg openings, right at the top of the openings.
Now you just need to knit back and forth, as if you has 2 straight needles in your hands. You are working the stitches that cover the 'butt' or back side, come between the legs and up the front. As you are decreasing at each end of every other row - that gives it the shape for the leg openings.
Like Mason says - if you were doing stockinette stitch on the circular part, you were knitting every round. After you break off the stitches to the holder you are now working flat rows, so to maintain the stockinette stitch, you will have to knit one row and then purl one row.