Typically, a page has at least two layers: one for the editorial content, and another for advertisement. Thus, editorial staff can work on the same page at the same time as the advertising staff. While editorial designers are laying down the editorial layer, advertisement staff can import ads onto advertisement layer.

An additional variant is when you want two designers to work on the same spread, while advertisement works on their layer. Thus, there will be three layers: two editorial layers, one for each side of the spread, and one advertisement layer.

 

Use the Table of Contents to find information. See also Using table of contents in help.