Typically when seeing a default Apache page, you are dealing with a scenario where the files of your application or site are not in the correct location, or if in the correct location, the web server is configured to look at a different index file other than the one you have installed ( index.php ).

Check out this article on installing WordPress on Ubuntu 14. The same principles apply in most configurations, and you are always able to customize the Document root and other configuration values to suite your particular style of deployment.

In some cases, it's also a good idea to start from scratch and make sure you got each part of the process completed properly. Hope that helps.

Make sure you remove the default Index.html in /var/www/html then make sure your defaults are .php and not html in either your .htaccess.

i.e.
DirectoryIndex index.php