Every document consists of one or more layers. There are two layers by default (background and foreground).
Each layer is an isolated space where you can place objects. Layers are stacked in structure. One can think of layers as transparent sheets placed one atop of another. You can look through the empty area of an upper layer and see the objects on the lower layer.
A layer is used to isolate a number of objects and manage their properties together. By changing a layer's properties, you affect all of the objects on it. For example, if you make a layer invisible, all of its objects become invisible.
The simplest page layout consists of pages that have one layer. This is similar to a regular text editor.
The page layout is defined by the selected paper.