The position of an element can be changed by just dragging it to the right position. But to make the publication perfectly aligned and set elements to fullscreen you will need to check out the position and alignment panel.
In this panel you will see the position of your elements and its width and height. Rotating your element is also something you can do in this panel. You can enter values manually or you can hover over the small button on the right side of the input field and start dragging up or down.
You can manually scale an element or you can set it to fullscreen. To do this change the top selectbox to fullscreen. Notice that some fields are greyed out because the element will make itself as big as possible inside your page.
The align tool is also very handy. Select multiple elements and make sure they align by clicking one of the button on the bottom of this panel.