This is going to sound dumb as I am a total noob. Do I have to save a page with PHP on it as a .php file. I have html pages and am wondering is there a way to make PHP work on a .html extension page? Or do I always have to save it as .php
One is to save your PHP scripts with filenames ending in .html and use either the AddType or AddHandler directive in .htaccess to tell your server that these files can also have PHP code in them.
The other way is to save the files as .php files and the server will know what to do with them, but in order to continue using .html URLs you will need to add a simple rewrite to the site configuration so that when .html URLs are requested, the server will use the matching .php file to deliver the content.
URLs and files are not at all the same thing. They are merely related by the action of a server in responding to URL requests. You can alter this action by changing the server configuration.