Just like publication pages, master pages can be a single page or two-page spread equally, and can be assigned to equivalent publication pages or spreads.
From default Document Setup, a master page will be created and applied to your publication page(s). After this, you can apply any new master page at any time using the Pages panel.
Master pages can be applied to other master pages in more complex documents. For example, a 'parent' master page containing just page numbering could be applied to multiple 'child' master pages coloured separately for each section. This means you only need to change the page numbering styling on the parent master page; also, as you create new pages you only need assign a child master page while inheriting page numbering automatically from its parent.
On a publication page, an assigned master page is actually a layer which shows in the Layers panel as a vertical solid orange marker prefixing the master page's layer entry; the expanded layer exposes the master page elements within.
Any master page elements edited on your publication page will show dashed orange markers on their layer entry.
By dragging a master layer to the top of your layer stack, you can present master page items above all other items in your publication.
Upon -clicking a master layer in the Layers panel, you can manage the master's destination (whether it is applied to the left/top, right/bottom, or both pages; available only for documents with facing pages), scaling behaviour and anchor position by selecting Properties. This will open the Master Placement dialog.
The following scaling behaviours are available:
Do one of the following, from the Pages panel:
Do one of the following: