combining 3d objects

i am doing a simple project of displaying a real-world object. For example, say I want to create a mineral bottle that’s basicallly made up of a cylinder, a half-sphere and another small cylinder for the cap.

So my question is, how to combine the 3d objects (cylinder, half-sphere, small cylinder) as one?

Code snippets will be helpful… thanks!

Well, either you already have the objects and want to show them at the same time, which is just a matter of rendering all of them, or you want to do solid modeling, which is not really an OpenGL question - in which case you might try the math forum.