@Renith_Harsan, Selemium is an open source project for web browser automation. It is primarily used in unit testing user interfaces during front end web application development.
My advice to you is go to the project page (http://www.seleniumhq.org/) and read the documentation. Just play with it! If you were to take up an job that needs it, you would need to explain where you have used it, how you have used it, etc… In my opinion, a certifcation in this may be a waste of your money.