Answer 1

Change the extension if the .html file to .php, and embed php code using <?php YOUR CODE ?>

Just keep in mind that you can't run php websites locally just by double clicking on them. You need to install a local webserver that supports php.

If you're on windows, I recommend WAMP or XAMPP. I think the Adobe Brackets editor has a web server built in that's capable of php, so you might be able to use Brackets to write your code, and use its live preview function.