A PHP file contains PHP code that is executed on the server. It typically has a .php extension. When accessed, the server processes the PHP code and outputs HTML to the user’s browser.

o run a PHP script, you need a web server (e.g., Apache, Nginx) with PHP installed. Save your script with a .php extension and place it in the web server’s root directory. You can access it via a web browser or run it from the command line using: php filename.php

Both are used to include files in PHP scripts. The difference is that require will produce a fatal error and stop the script if the file cannot be included, whereas include will only produce a warning, and the script will continue to execute.