What is basic need of xml transformation? In which situation we can use this ? can we use this in .Net?
Suppose you get several different product catalogues, each in a different XML format.
You use yet another XML format internally.
The simplest thing to do is transform the different XML formats to your own. You can use XSLT for that.
The .NET framework has extensive support from XSL transformations - see the System.Xml.Xsl namespace.
If you are working with data in XML format, you sooner or later need that data in a different format, need parts of it extracted, need it converted to HTML, simple text, another XML format etc. That's what XSLT is for. XSLT is a complete programming language. If you want to see some examples for the capabilities, look at the docbook XSL site.
However, sometimes it easier / more convenient to process your XML by other techniques. For example, in .NET you will also find the System.Xml.XmlDocument
class, which allows you to process XML data in another way, without using XSLT.