Like a Custom Title, the Custom Menu can greatly improve your Slideshow presentation.   Again the custom Menu is based on the information that you provided.  The Menu basically identifies the subject of a designated chapter.   Normally, you can have up to 6 chapters that can be selected within a Custom Menu.  Selection of the Chapter locations will result in going to the selected location within your presentation.   An example of a Custom Menu:  From the Main Menu, select "Epcot", this would result in Epcot menu being displayed, possible chapters could be "Soarin", another "Test Track" another "Space" or "Characters', then "Fireworks".   Actually think of a chapter as a chapter in a book, it has a story to tell.