How to work back and forth

Hi, I’m working on a sweater vest, and I had a question about using a circular needle. The pattern says:
DO NOT JOIN, Neck Ribbing will be worked back and forth.

How do you knit on circ needles and NOT join? I found similar questions on the forum that describe how you use the needles as though they were regular straight needles, but for some reason, I still can’t figure this out! Can anyone provide a clear and explicit description of how to work back and forth and not join yarn when using a circular needle? Thanks so much!

When you CO the stitches you turn the needle and knit with the empty one. At the end of that row, turn again and knit with the empty one. Just like when you knit with 2 straight needles. It’s not which needle you use, but how you use them that makes knitting flat or in the round.