Writing to an XML document

if I have an XML document on my server.
and Flash SENDS some data to it.
Now if I open that XML document, have its contents changed?

I’m sorry for such a basic question, but I’m failing. I know XML is incredibly useful and important and will probably help me out a great deal in many endeavors, but I have ZERO idea how it could at this point.

(yes I am a kirupa tutorial addict, and I’m in the middle of XML part2 right now.)