Displaying excerpts and thumbnails from posts created using a custom post type on a page

I installed CustomPress, made my first custom post type (shop_items) and created several posts within that type. Now I would like to get those shop_items posts to display on the main shop page. Currently the code that calls the posts on the main shop page is calling all the regular (non-custom) posts in the shop category, so I need to edit that php so that it calls all shop_items instead. Is there a tutorial or any resources that shows how to display all posts that belong to a custom post type? I searched the WPMU forums and didn’t find anything, but I wasn’t totally sure what to search for.