Like Jan says, it sounds like a hem. I can't find anything specific to picking up a stitch from the cast on edge but if you look here
and scroll down to Step 5, you might get a better idea of what you're doing. You could pickup the stitches at the cast on edge onto a second needles. Then the three needle bind-off Jan mentions would be next. There are two videos for it here,
one English and one Continental. Did your pattern call for a provisional cast on?