People might not understand the part about the arms, so here's the thing, as the arms are flat, they need to attach themselves to parts 19-20 (the shoulders) that's why the pieces 11 and 13 are there with the same color. Oh! and just repeat the process for the other arm. I just wanted to clear that out but in any case, if you still don't understand, the pdo is inside the .rar so you can see the 3D model instead of looking at photos.
Good luck! and enjoy!