First sweater (HELP!)

Hi there everybody!
I’m a beginning-ish knitter and have run into problems making my first sweater. I knit the body just fine (wasn’t that hard considering that it’s stockinette stitch!), but now I’m at the neck.
My directions tell me to:
Shape Neck: Next Row (RS): K11, join 2nd ball of yarn and bind off center 7 sts, k to end. Working both sides at once, bind off 3 sts from each neck edge once. Bind off remaining 8 sts each side for shoulders.
How exactly do I do that?
Do I add the yarn like I’m tying in a new piece?
And how do I work both sides at once?
I really need someone to spell this out for me!

Stay warm, those of you in the middle of the snowstorm!

After you knit 11 they have you jion a new ball of yarn to bind off the 7 sts because you need new ball of yarn to be able to knit the next set of sts.So you would K11 drop yarn you are using and add new ball bind off 7 knit to end .
Next row knit to bind off sts then drop that yarn and move to next set of sts and pick up that yarn and start knitting again. That is how you work both sides at once.You can’t use same ball of yarn because of bound off sts.

Thank you so much! I did what you said and the neck looks like I think it’s supposed to.