Knitting two pieces together

I am working on a sweater that has a back that is made in two pieces joined at center
The pattern reads as follows:After 3 1/8" leave all sts. Work 2nd back alike. (Work tog st for st idle sts of 1st back with idle sts of 2nd back, seam outside, bind off at the same time.)

What is not clear is the part in parenthesis. Do I bind off each stitch alternately off using 3 needles. Do I bind off from the right side of the work?

The instructions are a little confusing, but it sounds like they’re telling you to do a 3-needle bindoff where you are, essentially, knitting the shoulders together in a seam.

If that is, indeed, what you’re being told, then there is a video on this sight that will show you how to do this. Click on the Videos tab above, click on Casting off/Binding off and then on Three Needle Bind Off.

Hope that helps! Good Luck!

Thanks for the response so soon. The other part of the explanation is it is telling me to seam outside. What do you think that means (seam outside)