When you add objects to a page, they become ordered in layers. Think of it like pieces of paper stacked on top of each other on your desk. To bring an object forward or back, you right click on it and select what you want to do from the menu.

Now we do have a few issues with layering at the moment. The software sometimes gets a little confused as to what is on top of something else, so you need to Save then Preview your pages occasionally to make sure what-you-see-is-what-you-get, and you might have to play around with the layers a little bit to get them right. We're working on this!