Thanks for adding the picture, it's a bit hard to tell exactly which part you're referring to, but will give it a go.
As best I can tell we're looking from the lens-mount into the camera, and you've detached the focussing screen from where it normally sits (i.e. normally parallel with the base of the camera). At the bottom is the Reflex mirror, which is semi-transparent.
Between the mirror and the focussing screen may be the piece of metal you're referring to? I don't know the D3200 but it could either be a mechanism to hold the focussing screen in place (it may be interchangeable on this camera?) or perhaps part of the spring for the reflex screen.
Above the focussing screen will be the viewfinder optics, which is probably a lens, pentamirror and the viewfinder lens.
The Digital Single-Lens-Reflex Camera page on wikipedia has a good diagram to show the main common components in most DSLRs.