This video explains how PHP is used to generate HTML.
Initially, it is hard to grasp the concept that the browser only understands HTML and javascript. Yet when you view PHP source code you see passwords and other information you would NOT want users to know. PHP is an interpreter that the Apache server runs to evaluate files with a PHP extension. The output is the HTML that is sent back to the client browser.
I hope this video helps. Email me if you want an MS-Team Meeting to discuss this or any other CIT253 topic.