What is the best practice for linking two PHP files together?

When linking two PHP files together, the best practice is to use the `require` or `include` statement to include one file in another. This ensures that the code in the included file is executed within the context of the including file, allowing for seamless integration of functionality.

// File 1: index.php
<?php
require 'file2.php';
echo "This is file 1";
?>

// File 2: file2.php
<?php
echo "This is file 2";
?>