"Work from both sides" -??

[akeru1]

Hello from a semi-newbie who is knitting her first pullover vest!
http://www.berroco.com/exclusives/peter/peter_easy.html.
I'm working on the front panel, and have come to the instructions for shaping the armholes and neck:
"Bind off 8 sts, work until there are 45 sts on RH needle, sl center 2 sts onto holder, join another ball of yarn and k to end. Work both sides at once. On following row, bind off 8 sts, purl to end. Still working both sides at once, dec 1 st at each armhole edge every RS row 12 times. At the same time, dec 1 st at each neck edge every RS row 8 times, then every other RS row 8 times."
I understand up to the part about joining another ball of yarn...to WHAT? And I have NO idea about what "work both sides at once" means.
Any help would be much appreciated!! -K

[Ingrid]

"Bind off 8 sts, work until there are 45 sts on RH needle, sl center 2 sts onto holder, join another ball of yarn and k to end. Work both sides at once. On following row, bind off 8 sts, purl to end. Still working both sides at once, dec 1 st at each armhole edge every RS row 12 times. At the same time, dec 1 st at each neck edge every RS row 8 times, then every other RS row 8 times."

You're splitting the front into two sides--one for each shoulder.

You bind off for the underarm, put the center stitches onto a holder.

Then using a new ball of yarn, you work the rest of the stitches. You can just start knitting with it and then snug it up and weave in the end later.

Now you have a ball of yarn attached to each side.

You'll bind off 8 stitches at the beginning of the row for the other underarm, and work across each side with it's own ball of yarn.

Now you'll be decreasing at both ends of each side.

You'll knit 2 together at the armhole edges on every right side row, and also knit 2 together at each neck edge--basically at the beginning and end of each section for 8 right-side rows.

Then you'll continue to decrease at the armhole edge every knit row for 4 more rows, and at the neck edge every other right side edge for 8 more rows.

[akeru1]

Thank you, Ingrid! What a helpful (and fast) reply!