XML and data exchange

I am new to the use of xml and its use to exchange data between applications. I am planning to write an application that will get its input from an xml file, and I want the xml file to be validated using xml schemas. I am planning to host the application on a linux application server and I would like to program it in C. I am unsure as how to proceed when it comes to using xml for data exchange in applications, where do I start?

I have checked out the libxml2 site, but I don't really understand how to use the xml parser to split out data that the program can use and then output data in xml format with both the input and output xml files validated with an xml schema any help would be greatly appreciated, the kind of help I am looking for is just to get me started so I appologize if I am too vague