Trying to embed php in html [duplicate]

I don't know this is not echoing the "Hello world" in the php tags inside the html here.

  <div class="col-md-4">
          <span class="copyright">Copyright &copy; ... 2023</span>
<h1>blah<?php echo "Hello World"; ?></h1>
<h1> hello </h1>
        </div>

source https://stackoverflow.com/questions/75952380/trying-to-embed-php-in-html