[Where To Store Php Files?]

I am using PHP for the first time, and will be teaching it soon.
I am confused about where to store the PHP files.
 

Our I.T. dept set up Ubuntu 16, with Apache 2.4, and PHP 7.0

I can run the existing info.php from the var/www/html folder and see results using

  URL    http:// IPaddress /info.php

I can make html files and store them in ~username/public_html and see results using

  URL     http:// IPaddress /~username/whatever.html

But where do I (and eventually my students) store our PHP files?

They show as not found if I put them in the public_html folder.

And copying new files to the var/www/html folder gives a denied access error.

Do I need to get permissions changed so that I (and students) can store to var/www/html?

If so, how do I set it up so student A can't see (copy) student B's files?

Thanks, Steve