If the sleeves are flat, lay out the sweater face up and line up the sleeves so the center is at the shoulder seam. Then mattress stitch the sleeves to the sweater.
Do the sleeve seams the same way--mattress stitch.
Then, starting at the bottom, seam the sides.
Close the top of the hood.
After that, you should be able to see which row ends attach to the
stitches bound off at the center front--it's hard for me to picture without seeing it.
Then you sew the back of the hood to the neck.
Amy has video on mattress stitch, and www.knitty.com has a great article and pictures