As automation testers, many times, we reminisce about what is going on behind the scenes after the URL is passed to the web browser. What happens once the browser requests to load a website, or how does it know whether its request has been accepted and is ready to be fulfilled or not.
The answer to these is the HTTP response status codes for the resource APIs executed on the backend for the website. The request goes to the website server, which tells the browser through these numeric codes whether it is successful or not.