PHP code lives in files with the .php extension. The server processes them before sending HTML to the browser. PHP tags delimit code from HTML:

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

<!DOCTYPE html>
<html>
<body>
  <p><?php echo "The time is: " . date("H:i:s"); ?></p>
</body>
</html>

Test PHP from the command line without a web server:

php -r 'echo "Hello from CLI\n";\'
php my_script.php

Start the built-in development server, perfect for quick testing (never use in production):

php -S localhost:8080

View your PHP configuration including loaded extensions and php.ini path:

<?php phpinfo(); ?>