PHP pages MUST be named correctly (with .php)
PHP code needs to be within a special set of tags (?php ?) it tells the server that inside those tags interpret the PHP code.
First I would do a quick hello world explaining what PHP usually does is add content to the HTML page (show source of output?), and to do that you need to echo or print the data. You can also include formatting ...HTML formatting.
remember, all PHP code needs to be within in <?php ?>
<?php
echo "hello world";
?>
Mention you can have multiple php blocks, things are done sequentially, etc. The go onto variables, conditionals, etc.
The important part is start out with a simple success:
echo "hello world";