Ravi, first you must learn the syntax of the eXstensible Stylesheet Language and how an XSLT Engine operates. Then you need to learn how to write XSL code, e.g if statements, for loops, etc., using the XSL syntax. There are numerous books that will teach you XSL.
In case it isn't clear yet: XSLT is a programming language. You wouldn't post here and say "I need to write a Java program to convert this file format to that file format, but I don't know anything about Java, what should I do", would you?