Adding attachments to WordPress posts is not that hard. Displaying them is easy too as long as you know a bit of coding. List Related Attachments is a free plugin designed to make that job a tad bit easier. It is a sidebar widget and shortcode that can display post attachments. You can choose the number of attachment to display and their type.
List Related Attachments can show related attachments for a given post or page as a sorted and ordered list. You can change the order direction easily. You can download the plugin from WordPress.org.