Any PHP Script Starts with <?php and end with ?>.
Syntax:
<?php
// PHP Script here
?>
The PHP script must be saved with the file extension .PHP 
Comment in PHP code
A comment is a description that is placed for readers to make more clear. like other programming languages, PHP also has two types of comments.
  1. Single-line comment: used to put a comment for only single lines. A single-line comment in PHP script starts with either Hash(#) or Double forward-slash(//).
Example:
<?php
// This is a comment.
# This is also a comment.
echo "Hello World!";
?>
    2. Multiple-line Comment: Multiple line comments are used to provide a detailed explanation for readers which is more than one line and starts with /* and ends with */.
Example:

<?php
/* This is a multiple
line comment*/

echo "Hello World!";
?>