The neck and armhole edges are at their logical respective places. With the right side facing the public, hold the left or right front up against you. This is the easiest way to tell which is the armhole edge and which is the neck edge if you get confused.
To reverse shaping, work the shaping at the opposite end from where you worked it for the first side. Usually you will begin to shape an armhole by binding off stitches. If you bound off the stitches at the beginning of a right side row for one front, you would bind off stitches at the beginning of a wrong side row for the other front. This keep the shaping on the correct edge.
If you are increasing or decreasing at the beginning of a row for one front, you would increase or decrease at the end of the row for the other front.
Got that from this website
Also more simply put from the dummies website
If you work the shaping on the wrong side in one piece, you'll work it on the right side when you reverse the shaping.
Hope this helps it helped me a bit. I had the same question.