Each time you start PowerPoint, it displays a temporary presentation, just as Microsoft Word displays a blank document and Microsoft Excel a blank workbook. You can create a plain, blank presentation from within PowerPoint by clicking New Presentation on the File menu (or pressing Command+N).
Alternatively, you can create a presentation that already has an Office theme applied, or a pre-populated presentation, by clicking Project Gallery on the File menu.
The new presentation, whether blank, themed, or pre-populated, is a temporary file until you save it. If you close the file without saving it, the file and its contents will be entirely removed from the computer.
For information about creating presentations that are already formatted with a graphic theme, see "Create a Presentation Based on an Office Theme Template" later in this chapter.