COM is a standard for developing reusable, modular components. Microsoft has developed this standard so that creators and users of these reusable components speak a common language. A COM object exposes one or more interfaces. Each interface is a collection of semantically related functions. You may think of an interface as a set of services that will let you perform useful actions such as finding the names of all the computers in a particular network domain. DirectScript includes COM objects that you can use from Visual Basic scripts, JScript or Visual C++.
You can find detailed information on COM from sources mentioned below:
Documentation on COM under Win32 SDK/OLE
Inside OLE, 2nd edition, Kraig Brockschmidt, Microsoft Press
The documentation accompanying Visual Basic explains how COM servers and clients can be created using Visual Basic.