How to display portfolio or other post types on the page
The images that are displayed on the portfolio element are portfolio items, they are linked through categories to the portfolio element. The images that are displayed for the portfolio item are placed on featured image of each portfolio item. The same is for the posts and products, the only difference is the post type you select in the posts element.
The following example shows a posts element in which are attached 'Apps', 'Development' and 'Editing' categories, which means all the portfolio items that have assigned one of these categories will be directly displayed on that page.
There is also the Metro Layout Type in which the posts are manually added via query field, the reason why they are manually added there is because of their columns flexibility.