You can create a new master from scratch or from an existing master page or spread. After you apply master pages to other pages, any changes made to the source master carry forward to the masters and document pages that are based on it. With careful planning, this provides an easy way to make layout changes to multiple pages across your document.
For a video on working with master pages, see www.adobe.com/go/vid0069.
For Prefix, type a prefix that identifies the applied master for each page in the Pages panel. You can type as many as four characters.
For Name, type a name for the master spread.
For Based on Master, choose an existing master spread on which you’ll base this master spread (see Base one master on another), or choose None.
For Number of Pages, type a value for the number of pages you want in the master spread (as many as ten).
Any objects on the original page or spread become part of the new master. If the original page used a master, the new master is based on the original page’s master.