You can add an item by pressing the 'New' button on the page itself.
Each item can have multiple image, a title, a text for in the overview and a (longer) text for the detail page. You can also enter meta keywords and a description for each item.
One main image can be shown in the overview list, the rest will be shown on the detail page. You can select the main image by adding one or more images and then clicking one of them. The corner will turn blue to show it has been selected. To unselect an image simply click it again, you can then select another image.
Changing the order
You can change the order of items in the overview by dragging them up or down on the page itself.