PowerPoint uses a variety of built-in Themes that are installed by default. Themes can also be saved from within Microsoft Word and Excel (version 2010) in the same way it is done in PowerPoint. In both of these programs, Themes are found in a tab location different from that of PowerPoint.
To learn more, choose your version of PowerPoint. If we do not have a tutorial for your version of PowerPoint, explore the version closest to the one you use.