Question about Metro "Knit Deep V Sweater"

:?? Ok, I’m stumped. This pattern is at I don’t get what this means:

“With right side facing, join yarn and bind off center 13 (15, 15) sts…” How do you ‘join yarn’? Thanks for your help.

Use a new ball of yarn (or the old one if you’re done with it) and just start knitting and binding off. It will be secured in the process of binding off, and you’ll likely be working the two shoulders now.