Example - different header for pages.

header.php

<?php // Reference: https://codex.wordpress.org/Conditional_Tags 
      // Use conditional PHP tags to ouput different content based on the template in use?>

<?php if ( is_page ) ) : // check if we are on a page ?>

      <?php // code here for display on pages ?>

<?php else : // code below runs if we are NOT on a page ?>
      
      <?php // code here displays on anything that is NOT a page ?>
      <?php // put any HTML / php here that you want to show on non-pages ?>

<?php endif; ?>