l want use PHP inside HTML. How Do i do that

Answer 1

instead of .html file use .php file. If you want to write some code just use

<?php
//your code
?>

Answer 2

By default config if file extension is html not posible use php code inside. Code is not executed.

Easy way: rename the file to .php and open tag like a <?php .... ?>

Hard and insecure way, you can change the config to execute all .html files like a php file.

I think, you want the first option.