Layout
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 imagine layers as transparent sheets placed one atop of another. You can see 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.
To any regular page (content page), you can assign a master page. It contains its own layer stack. A master page, when it is assigned, is always located behind the bottommost layer of the content page. Normally, the content pages are used for regular objects (text and graphics). Master pages are used for objects that appear in the same place on multiple pages (page numbers, background decoration and so on).
The simplest page layout consists of content pages (with no master) that have one layer. This is similar to a regular text editor. A sophisticated layout can include a content page with several layers, and a master page that contains its own layers.
The stack of layers is the same for all pages of the document. This means that if you add a new layer to any content page, this layer will appear on all other pages, including master pages. If you hide a layer, objects on this layer disappear on all pages.