Appium is used only for testing mobile applications either android or iOS testing having Android and iOS Driver. Users can directly connect android or iOS device and run or test application over it or can use virtual device.
On the other hand Selenium is used to implement and run automation test scripts of web applications. Both Appium and Selenium are customized and open-source this a common thing between them this feature enables the users to use according to their requirements. If you are looking for a professional certificate in Selenium then you must have a look at the following Selenium Training Course. You should also watch the below-mentioned video on Selenium to clear all your basic doubts regarding it..