Need help w/sweater back, binding off and joining at same time?

I have never knitted a sweater before. I am almost to the top of the back piece and it says:[B]Shape shoulder and neck:[B]/bind off 9 (I know how to do that). Work next 23 sts (still okay) Join 2nd ball of yarn (which I think I understand how to do), (now is the part I don’t exactly understand) and bind off next 22 sts. Work to end of row. Work in 2 halves with these separate balls

I don’t understand how to join and bind off at the same time? I would join by leaving a tail on the old ball and a tail on the new ball and weave in the tails later. How do I join and bind off on the same stitch? Also, can you give me a little help on how to work in 2 halves? This is a pattern of a sweater with a flap for a collar, fyi.
thanks for any and all help!

Join the new ball just as you say, leaving a tail of the old ball and a tail of the new and just knitting with the new ball. You’ll knit two sts to begin the bind off and then slip the first st over the second on the right needle and continue to bind off. Don’t worry about loose sts where the new ball is joined, you can tighten up those sts at any time.
When you work in halves, you’ll knit with one ball of yarn up to the join or bind off, drop that ball, pick up the second ball of yarn and work the second half with that ball of yarn. It’s like knitting two separate pieces each with its own yarn ball but on the same needle.