Can you tell us how you want to store the xml in the database, and what you want to do with that data later?
Please show us what you have already tried.
How large is the XML data? What is the maximum size of a string that can be stored in your database? If the latter is greater than the former, you can store the XML in a string column. Otherwise use a CLOB.
Not directly without some form of transformation. It's a bit like apples and oranges when comparing XML and database data. You need an application to map one to the other else you may have a lot of denormalized data.