Maybe it would help more if I wasn't so vague!!
I am knitting a purse. I have done the strap first, and used provisional cast on for that part. So I have my long strap piece with live stitches on either end. That part is fine. So then what I want to do is join it all in the round and knit the bag from the top down, AND knit in the two ends of the strap where they would be placed, so I don't have to do any seaming.
So I want to cast on the stitches for the front of the bag onto my circular needle, then knit off the holder the one half of live stitches, then cast on the stitches for the back of the bag, then knit off the holder the second half of live stitches, then start knitting in the round.
Does that make a bit more sense?