Ok . the 2 pieces are sleves , you want to sew the sides first. then you will do the sleeves. they are little puff sleeves. then you need a zipper . you will be able to see how the collar is once you get the sleeves on. to me this needs a lining or a partial lining. I keep looking at your pic. diffently need linning on your collar parts.
try sewing , sides back about 4 to 6 inches then look to see how the shoulders match . sew top of shoulders . sew each sleeve the 2 small straight part together.
then match up to sleeve holes. start from the bottom of the sleeve first . you need a needle and thread to make the pucker for the puff of the sleeve. you should be able to figure out the rest . if you need help let me know