Building Distributed Application

i want to begin build distributed application
what subjects i need to read/learn

This question is extremely broad, which means it is very difficult to give a good answer in a few lines. So any answer will also be very broad.

1. How computers work
2. How networks work
3. The different types of networks
4. A programming language (in this case, I suggest C++ if you want to use Qt, or Python)
5. Also, in this case I suggest learning a library like Qt.
6. How to test software and how to debug it
7. ...

i know C++/Qt good
and i design Business Application and i want to make it client/server application
can i use QWebkit or what i need to learn first
can i use web services with Qt if yes how can i do that ??
thank you

Do you want to make it a client/server application. Or do you need to?

If you want to create a client and a server, how do you want them to communicate?

i have regular database application for company and i want to make it distributed application to install it in company branches

can i use Network programming for this purpose or there are another ways like Web Services (SOAP say)