Let’s first talk about TestNG, it is a framework which will help you organize your tests ex: prioritizing, retrying, reporting etc. Where as Selenium cannot do this. Selenium also gives you a WebDriver API through which you can identify and act on certain elements on your Web application. But it cannot generate reports or tabulate and organize results, retry a test case etc. So it has to use a framework and TestNG comes into the picture. If you want to learn Selenium you must take up the following Selenium Training Course. You can also watch the following Selenium video tutorial which you must watch to learn more about it.