A part's inner structure does not become clear directly from the 3D view. Furthermore parts have detailed additional information, which indicates the precise use.
The following points should give an overview on a range of helpful functions.
Click with the middle mouse key in order to set some single parts to transparent.
Click on the respective toolbar icon in order to activate the "Exploded view".
Click on the respective toolbar icon in order to activate the "Assembly structure" feature.
The bill of material can be found in the docking window Assembly.
Often additional information is linked in the characteristic attribute table.