This dialog can be reached by opening the context menu for an element and selecting "Change Position" or pressing F5 on a selected element. You can use this dialog to set exact location and size of elements. Usually you can set the following properties for the element:
The left position on the x-axis.
The top position on the y-axis (starting at the beginning of the section).
The width of the element.
The height of the element.
Please note that the dialog will have some restrictions for some type of elements: