If you can translate from C#.NET, there is a large sample source code project at the following link, which gives you examples for interacting with a large number of C3D objects using a .NET language.
The big point of confusion is that, while there is a .NET API for the core vanilla Autocad functionality, there is no .NET API for the C3D stuff. So all the C3D interactions actually use COM objects. That's why there's a lot of converting between DBObjects and AcadObjects.
http://www.quux.biz/SincpacC3D_source.aspx
Sinc