Before you start customizing, it's important to know that some automatic adjustments to menus and toolbars occur in Office programs.
When you first start an Office program, only the most basic commands appear. Then, as you work, the menus and toolbars adjust so that only the commands and buttons you use most often appear. If a command or button is not used for a certain amount of time, it "drops off" the menu or toolbar. Office is adapting to the way you work and is trying to customize for you.
Before changing any default toolbars or menus you should think carefully about what you are trying to achieve. Altering existing toolbars or menus could make it difficult to perform tasks and follow instructions in other courses, books, and Help, as they will all refer to the standard configurations of Office programs. Perhaps leaving the existing features alone and creating your own new toolbars or menus is the better option.
Also, consider whether your Office programs might have already been customized by your company's system administrator. If so, you might change something and not be able to get it back. Resetting toolbars and menus returns them to the default settings that were designed for Office, not to how they were when you started.
Although this course discusses the most common ways of customizing, you can learn more about specific customization in each product's Help topics.