What is COM?

I am new to VB6.
I want to learn COM conepts and how to use com practically?
why are we using COM?
Could you please give some input based COM?

I'm a little surprised this web page still exists. Most of the links I've accumulated over the years for VB6 are gone now because VB6 has not been a supported language for a few years.

If you are new to programming I would STRONGLY suggest getting into VB.NET (and its COM features and capabilities)

However, since you did ask about VB6, and this page is still there, I'll give you the link.

http://www.vbexplorer.com/VBExplorer/wrox/vbcomsamp.asp

I need some sample code with an example to understand better than the theory.

VB6 effectively is a BASIC interface to Microsoft's (C)omponent (O)bject (M)odel platform - in many ways VB6 is (was) the ultimate COM beasty.

It is still widely used, although most of the code is now written in C++ for the reasons Hack explained - VB6 is virtually not supported now; and there are plenty of unfixed bugs in the VB6 compiler - and the O/S teams really do not care for the unmanaged code anymore - try some registry Win32 API's working on Windows Server 2008 R2!

Unless you are supporting legacy code, opt for the .Net platform.