Looking at the pattern again, you're dividing the neck. So you're knitting the 13 stitches from the arm edge to the middle of the cable. Then you turn your work around as if you finished the row. Your yarn will be on the left needle as it is when you start any new row. The stitches left on the needle will be for the other side of the neck/shoulder. Many patterns have you put the unworked stitches on a holder, but this just leaves them on the needle to be worked later.
By doing it this way, you will be creating the two halves of the v-neck.