You mean this image? https://world.mendix.com/download/attachments/2621450/ImageEntity3.png?version=1&modificationDate=1282133081000&api=v2
That's the TemplateGrid being used. In it's settings you can define how many columns or rows to show.
As for your other question: A Change Object is done on the NewPizza object, and in that Change action, the reference between NewPizza and NewPizzaImage is set.