Save ListView item in XML file

Question

Hello dear all ,
Am still working on my first C# winforms application .
I populate a list view with data from a XML file .
My xml file is like this

<?xml version="1.0" encoding="UTF-8"?>
<source rt="2012"   ez= "123">
<category active="0" attribut1="vrai" titre="aaaaaa">
    <category_value titre="acac">
      <object  background_colour="230" id="0" name="zzzzzz"  type="0">
        <child id="121" x="2" y="0" />
        <child id="131" x="3" y="0" />
      </object>
</category_value>
</<category>
</source>


am using the function in my document join

I need to do somthing but i dont know how I strart , it's possible to choose one or some item then when we clic on a new bouton we write this items in a new xml file ( similar to my XML file with only the items choosen )  or add them to an existed XML file ?  What is the easy way to do it ?  ( am really a big starter )


this function is important for my application , but i dont find somthing in the net to start with it

thank u all