Approaches to testing seem to be getting more important as the need for web applications comes into sharper focus. A tool for testing web applications has been Selenium, which is an open-source tool for automated testing. This paper presents valuable information regarding Selenium such as its structure, functions, opportunities, disadvantages, and comparison with other programs and instruments. Understanding of these factors gives testers a tool to make a proper choice concerning the degree of usage of Selenium for Web Automation. Selenium cross-browser compatibility makes it more useful than other testing tools and help in testing websites on various browsers. There are also some challenges faced by the tester while using selenium such as testing dynamic web element.