Short rows for pants


I’m trying to knit a pair of baby pants and got confused about the instructions.

The pants are knitted from the legs up. The legs are knitted separately and the stitches are put on 1 needle. Then cast on new stitches for the crotch…[B]How to cast on in the middle of the needle?
Then the back instruction is given as follows:

“Divide the work in the middle of the legs and work over the back sts. While doing so rest in every 2nd rnd 3 x 3 sts, in doing so work shortened rnds. Then cont working again over all sts in rnds k1 p1 alternatingly, while Ktog the YOs of the shortened rows”

Those are the exact words. It sounds like I’m supposed to knit the back with short rows but when do I turn? How many stitches are in the short row? Not sure what they meant by “middle of the legs” either…

Thanks in advance!

Cable or knit cast on the new sts by switching the needles in your hands and casting the new sta onto the left hand needle. When finished, switch the needles back again in your hands and continue the row.
The pattern wants you to divide front from back at what would be the side seams on a pair of pants.
For the short rows, work to three sts from rhe end of row and repeat on the next row. On the following rows continue to work three fewer sts in each short row.