Gravity Forms custom fields output

I'm trying to Output a user submitted Gravity Form embedded picture as a post thumbnail/ featured image using the the custom field from post fields. Now I'm having trouble outputting it on my index page as a clickable image. I found the code that I think does it, but don't really know how it works inorder to insert it into my index template

The Custom field name is Thumbnail_URL.

Ideally I'll want the code to be somewhat like this,

<?php if ( get_post_meta( get_the_ID(), 'thumb', true ) ) : ?>
    <a href="<?php the_permalink() ?>" rel="bookmark">
        <img class="thumb" src="<?php echo get_post_meta( get_the_ID(), 'thumb', true ) ?>" alt="<?php the_title(); ?>" />
<?php endif; ?>

but for now I just want to start by just seeing the data on my index with the code that's in the link(note I stripped the content template tag from my index cause I just want an clickable thumb and title)

Thank you for any help I receive :slight_smile: