TinyXML2: A Convenient C++ XML Library
High Level explanations, followed by examples with convenient code snippets with error checking
What it does.
In brief, TinyXML-2 parses an XML document, and builds from that a Document Object Model (DOM) that can be read, modified, and saved. 
What is XML?
XML stands for “eXtensible Markup Language.” It is a general purpose human and machine readable markup language to describe arbitrary data.