You can Selenium tests in two ways in multiple browsers which are as follows:-
Use TestNG to pass parameters annotation and convert .xml<file>.
Selenium grid is a process to run multiple devices/browsers.
And the much better way to run tests multiple devices/browsers in the cloud(providing thousands of devices/browsers) using the single platform “Test Sigma”. supports multiple applications (web,mobile web,Android/iOS native, RestFul Services) also. If you want to learn Selenium you must take up the following Selenium training Course. You can also watch the following Selenium tutorial which you must watch to clear all your doubts regarding Selenium.