Layers allow you to assemble elements on a page that are related. Think of layers as individual workspaces that you can hide from view, hide from printing, or lock.
Layers do not determine the stacking order of objects on your page, except for the Controls layer which is always in front of other layers.
The stacking order of objects on your page is determined by the sequence in which you add the objects. You can rearrange the stacking order by Shape - Arrange.
The areas on a layer that do not contain objects are transparent.
LibreOffice Draw provides three default layers:
You cannot delete or rename the default layers. You can add your own layers by Insert - Layer.
The Layout layer is the default workspace. The Layout layer determines the location of title, text, and object placeholders on your page.
The Controls layer can be used for buttons that have been assigned an action, but that should not be printed. Set the layer's properties to not printable. Objects on the Controls layer are always in front of objects on other layers.
The Dimension Lines layer is where you draw, for example, the dimension lines. By switching the layer to show or hide, you can easily switch these lines on and off.