I want to know, How to create a web service and how to use it. Thanks very much.
Well if you're really patient and want to learn this properly I suggest you check out
MSDN.
How Web Services actually work can get pretty complicated...they use Soap, which is based on XML to send information to and from your Web Service.
The Web Service itself is really just a bunch of functions hosted on the web that you can access from your desktop application or web application written in any language.
They are really powerful! Mainly because you can write a function in C# and host it as a Web Service..then you can use it in a Java application or VB application... or even Cobol.
.NET makes it pretty easy though.
I'd suggest looking up Web Services with Google to get started....there are plenty of tutorials out there to get you started.
-Frinny