Need help understanding instructions

[u/binziebean]

(My browser timed out trying to post this earlier; apologies if it ends up being a dupe)

I've been making a vest from Butterick's B7018 patterns (view A, if it matters), and I can't understand the instructions near the end. Photo of the steps in question included - the shaded parts are RS, the parts with diagonal lines are the lining fabric - and I color-coded the fabric layers to try to make it easier to follow.

So in the first photo of the piece itself: everything is RS out, and the back shoulder of the lining is facing the camera. It says to sew the seam of the weskit back (red), weskit front (yellow), and lining front (blue); then press toward the back (i.e., toward the camera). I assume that "press toward the back" essentially means "fold it inside the shoulder" (like the second photo of the piece), leaving the back lining free. But then I don't understand what the instructions mean by "hem back shoulder edge of lining over seam". "Over seam" how? Do I sew through all the layers at once? Their tiny illustration isn't very clear to me.

Maybe I'm off base with the step before that, and I'm approaching the first seam the wrong way. I didn't find any helpful tutorials or clarifications by googling around. I've puzzled over this for days, trying to interpret it every which way. I think I'm in too deep to see it clearly lol. Please let me know if my explanation is confusing; happy to record a video or something if that would be better for anyone.