Here's a little something I threw together for you to give you an idea of one method. I just took a cylinder and applied a bevel. then I extruded the sides about half the distance between two joints. Then after all cylinders were extruded, I merged all the joints together. Then I used the cut face tool to cut two lines down the center (length of arm). I selected all the faces in between the two lines and then extruded outward to create the seam.

This is just to get you started in the right direction. There are other ways to model the arms but this is probably the easiest way. If you have trouble with extruding, then you could probably just create the three joints. Then create two cubes for the lower and upper arm and just have them sticking into the joints. Instead of one piece of geometry, you would have 5 pieces.

Good luck tgage!

P.S. I recommend moving this to the WIP section.