This Model is Supposed to Resemble the HOVI Mic Tips found on the Stormtrooper's Helmet in the Original Star Wars Trilogy. the small cylinder piece should be bolted to the helmet as an attach point for the greeble itself. The small round piece should be put into the Larger Mic piece through the bottom, which can then be fit onto the cylidrical attachment piece.
I'd suggest printing this at the maximum resolution to pick up as much detail as possible since these are some fairly small pieces and could be kind of a pain to sand after printing (I learned this the hard way). I would also suggest starting with a higher grit sandpaper (125-200) to avoid sanding off too much of the detail, hitting it with a coat or two of filler primer, sand the surface with a higher grit sandpaper and/or fine steel wool (#000 or #0000), and repeat until it's at its desired smoothness.