php in html

HTML
Basic PHP Syntax
A PHP script can be placed anywhere in the document.

A PHP script starts with <?php and ends with ?>:

<?php
// PHP code goes here
?>
The default file extension for PHP files is ".php".

A PHP file normally contains HTML tags, and some PHP scripting code.
  
Example
<!DOCTYPE html>
<html>
<body>

<h1>Php in html</h1>

<?php
echo "Hello World!";
?>

</body>
</html>
Source

Also in HTML: