what’s the syntax for if the image exists get the image?

It’s not completely clear if you want to show one image or all image for each post. If you want to show just one, I’d use the post thumbnail:

• Check for a post thumbnail. If there’s a post thumbnail – output it (for simplicity I’m assuming you’d output it in a new template part; you could simply include it inline using the_post_thumbnail());
• Otherwise include the post as currently (or a placeholder image if you’d prefer).

if(get_post_thumbnail_id()):
get_template_part('item-image-only');
else:
// fallback
endif;

If you need to output all images, you can use get_children – e.g. :

$attached_images = get_children( array(
'post_parent' => $post->ID ,
'post_status' => 'inherit',
'post_type' => 'attachment',
'post_mime_type' => 'image',
'order' => 'ASC',
'orderby' => 'menu_order') );

(and you can then check if an item has images by checking count($attached_images))