How Do I Generate A Xml File With Repect To User Input In Asp.Net?

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ASP.NET

XML

Hey,okay so i need help with this,consider a simple example:
say i have a 3 rich controls like:drop-down,calender and textbox.
User gives input to all three of them(for example:name of product(textbox),date of purchase(calender) and some product category(dropdownlist))
Now there is a button down below which has to generate XML file,how do i do it?

PS: All of this is in asp.net