Essentially Themes are like a style sheet for your Office documents. They define how your text appears, where it appears, and also the layouts of your slides. Themes also influence how charts look within Excel and PowerPoint, and also how your tables appear in all Office programs. You can also change the Theme for an Office document, sheet, or slide and watch how this simple task can change the overall appearance of your content.
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.