Hi Norton, welcome to the site.
Try thinking of it this way.
At the simplest level, PHP is a scripting language used to print out text to a browser. The text that PHP prints out is HTML.
Why use PHP? well, there are a ton of reasons yet most would be specific to what you are trying to accomplish.
One example is code re-use. You know that navigation you probably have on your site? Well, with pure HTML, if you need to change a link, you need to modify the same code on every single file that uses it.
With PHP, you can put your navigation HTML in one file, and include that file in all your pages. When the navigation changes, you just change one file.
nav.php
example:
PHP Code:
<a href="1.php">Nav 1</a>
<a href="2.php">Nav 2</a>
<a href="3.php">Nav 3</a>
notice, HTML can go in .php files. generally you just name all your files .php even if they are primarily HTML. that's so you can insert PHP code when needed.
so here is where it all ties in.
mypage.php
PHP Code:
<html>
<body>
<?php
// this code below inserts nav.php as if that file were pasted
// directly into this HTML
include("nav.php");
?>
.. rest of the HTML goes here
</body>
</html>
So the point is, I can have 100 pages which share this same nav. When I need to modify the nav, I can simply change nav.php.
This is just one example I picked because I remember how neat I thought that was when I first started using PHP a long time ago.
Hope that helps. Don't hesitate to use this forum as you develop your PHP skills .. We have pretty good support here on that topic.