What you are doing here is overriding the internet's domain name system, so that when you type www.web_address_here.com http://www.web_address_here.com into a browser, it will send you to the new server.
Ok that's it. You should now automatically be routed to the ip address you entered. When you're ready to stop routing to the given ip address simply go back to the file and delete the line you added.