back neck-shaping on v-neck vest
I'm new and need help understanding the shoulder & neck shaping on the back of a men's v-neck vest. I've completed the back & armhole shaping and am stuck on the next set of instructions for the shoulder & neck shaping. The instructions say to bind off 8 sts at the shoulder edge and work to the marker. Then I'm supposed to join a new ball of yarn and bind off the center 35 sts and work the remaining sts (to the end of the row). Why, how & where am I supposed to join the new ball of yarn? Then I'm supposed to work both sides separately but at the same time by binding off 8 sts at the shoulder edge and dec 2 sts at each neck edge 3 times. I understand how to do the stitches, but I'm confused by the yarn joining and working both sides "separately and at the same time". Can anyone clarify these instructions for me? I found a similar post, but it doesn't address the yarn joining. I'm trying to finish this for my dad before the holidays, so anyone help would be greatly appreciated!!!