This page is used to test the proper operation of the Apache HTTP server after it has been installed. If you can read this page it means that this site is working properly. However, you have not yet added any content.
The fact that you are seeing this page indicates that the website you just visited is either experiencing problems, or is undergoing routine maintenance.
You may now add content to the directory /var/www/html/. Note that until you do so, people visiting your website will see this page, and not your content.