I think I've got it...
I think I have some clues about the translation below:
First it's just to seam the longer side of the sleeve to the back.
Then you sew the collar with the points arrière on the right side of the work, as in the picture here on the right (from a French knitting magazine).
Then it says to sew the button allowance piece to the front and collar, inverting the seam, so it won't show when you wear the flap down.
Then the tricky part with another color and everything: First you knit one row from the right side and then some rows of stockinette in another color, and then you iron them, for blocking. You knit in another color just so you easily can frog and get an unfinished row for the points arrière.