Sleeves on a sweater

I have finished the front and back of a baby sweater. I am about to start the sleeves and here are my directions…"With new needles and right side facing,“pick up and knit 50 sts between armhole markers”.

Do the directions mean to push my needle through the already knit :guyknitting: front and back armhole thread until I have 50 sts on my new needle???
or
Do I just cast on 50 new sts and will attach to armhole later?
Bill

http://www.knittinghelp.com/apps/flash/video_player/play/166/1

The sleeves are knit on to the sweater to save you the trouble of seaming. You’ll be picking up stitches all around the edge of the sleeve hole to create the stitches to start working the sleeve from top to bottom. Check out the link on picking up stitches if you’re not sure how.

Take the sweater in your left hand and pretend it’s a needle. Insert the right needle into a stitch of the sweater, and wrap the yarn around it as if you were knitting, pull the yarn through. Repeat. You’ll have stitches on the right needle and the body’s attached to them. Oh, you need to sew the front and back together if they’re not already knit in one piece.