Summarize:

Though the pattern is only drawn on the top, make sure to cut through both layers. Then sew up the open side in a gentle arc around the dark ends; the dark ends will become the paws and the opposites (open ends) are where the arm will be stuffed and then attached to the body. Keep all of these sections open-ended. Make sure they're turned inside-out as you work! If they're not, all your seams will be very, very rough. Then sew up the open side and in a gentle arc around the dark end as you did with the arms; the dark end will become the tip of the tail and the opposite, open end is where the tail will be stuffed and attached to the body. Then, sew in a gentle arc following the rounded sides, leaving the flat side open. The opening is where you will stuff each ear and then attach it to the body. Noticing a pattern? If you'd like, you can then fold the ears again, forming a vertical line down the middle of the ear (giving it depth like a real ear has). Basically, pinch the edge you just sewed in and bring the two points together. Slip stitch the two sides together. That part's saved for later. You should now have two arms, two ears, a tail, and an unsewn, unstuffed nose. The tail may prove to be a bit of a problem. You could try to stuff it using regular polyfill stuffing and a pencil to poke it through, or you could use batting or part of an aquarium filter. Both the batting and the filter are a bit firmer and will create a more uniform-looking tail in the long run. Position it carefully and slip stitch it all the way around. You may want them a little higher than your natural inclination says; this will give your sock a more monkey-like posture.
Cut the second sock into sections as shown. Fold both arm pieces in half lengthwise. Fold the tailpiece in half lengthwise. Fold each ear in half and cut across the crease. For now, do nothing with the muzzle (formerly the heel). Flip the sewn pieces right-side out and stuff them. Attach the tail to the rump. Attach the arms to either side of the body.