That is a very broad and generic question.
Use XML for what exactly? What business requirements need to be addressed?
There is a wide range of XML functionality in Oracle. From using XML SQL functions to produce XML output from SQL cursors. To using XDB, registering XSDs, and generating SQL advance data types for the XML objects defined by the XSD.
This is not something simplistic with a narrow scope that you can expect someone to throw a source code example for you, in order for you to grok Oracle's XML functionality.
the oracle documentation provides so much information that I dont know where to start.
What about starting at the beginning?
Oracle manuals are designed just like any other manuals, with an introduction about the concepts and other general information, then they go into more specific/advanced stuff in subsequent chapters.
Here's the table of contents of the XML DB Dev Guide : Contents
Start by reading part 1 (the basics), then you can further read about specific tasks (generating, storing, parsing XML etc.) in the next chapters.