To understand the application and test the application manually and automatically.
Selenium created a new revolution in the automation testing industry. Selenium is open source, free of cost. It is a very powerful tool for automating our web based applications. Selenium supports Java and few other languages but Java is most commonly used in Selenium. Selenium provides full-control over automation testing using powerful frameworks including Selenium WebDriver/Junit. Another good thing about this tools is that it can run against multiple browsers.