First add an image to the hello world blog post. Edit the blog post in the WordPress Dashboard and add a Featured Image, as shown in the following screenshot:
Make sure that your WordPress installation has a writable
wp-content/uploads directory to store the uploaded media. Also see https://codex.wordpress.org/Changing_File_Permissions for more information about file permissions.
Now edit the
loop-archive.php file so that the HTML and PHP code looks like that shown here:
<article id="post-<?php the_ID(); ?>" <?php post_class(''); ?> role="article"> <?php the_post_thumbnail('full'); ?> <div class="blog-post"> <header class="article-header"> ...