The Selenium Server launches and kills browsers and acts as an HTTP

proxy for browser requests.

Client libraries for various programming languages, each of which

instructs the Selenium Server in how to test the AUT by passing it your

test script’s Selenium commands.

The client libraries communicate with the Server passing each Selenium

command for execution. Then the server passes the Selenium command to

the browser using Selenium-Core JavaScript commands. The browser, using

its JavaScript interpreter, executes the Selenium command, which

effectively, runs the check you specified in your Selenese test script.