can anybody tell me how to use WebParseDataBoundEx function and where exactly to use this function and what is the major use of this function
Try reading the Advanced Concepts document that comes with the install of SP.
But in the end doesn't it all come down to BEER? Beer is the ultimate answer to all questions in the universe so yes the answer to your question is BEER.
You use the function to retrieve data from the page in question. Most likely to extract a piece of data, like a session ID, or something like that to be re-sent on the next page.
You use it when Silk Performer isn't going to automatically send back the info you need.
I use it at times when I need to extract the title of a link that will vary from login to login.