"Getting the navigation right is one of the most important aspects of design. Navigation is the framework within which screens, interaction, and the visual appearance are designed. The most basic axiom of usability is that one should make interaction with the software as easy as possible, allowing users to focus on the tasks that brought them to the software in the first place. To the extent that navigation is confusing and requires the user's attention to figure it out, usability will suffer.
Navigation Is a Metaphor
The term "navigation" conveys the idea of traveling from place to place. It suggests that there are paths you follow to get from point to point and an underlying framework that directs (and restricts) how you get there. Yet, although we talk freely about navigating through a software product, we never actually go anywhere. We stay in one place while the image on the screen changes in response to our interactions with it. So "navigation" is really a metaphor, a mental game we play to get our minds around the design.
When most people think about navigation, they focus on menus as the way to move from screen to screen. But it is quite possible to write powerful programs built around a single screen. Think about Microsoft Word, for example. Despite its extensive and powerful functionality, almost the entire program is built around a single screen, as you see in Figure 1.
The document being worked on is central in the screen design. Tools selected from the Ribbon are applied to the document and change its content or appearance. When a tool requires a complex interaction, it typically pops up a child window over the document. The child window may be a modal one in which the user must complete the interaction and dismiss the child window before returning to the document—an example is the insert picture command. It might be a wizard that walks the user through a process. Alternatively, the child window may be modeless, like the Thesaurus command, in which case it is docked on the side where it can remain open while the user works on the document." (Continued via MSDN Magazine, Charles Kreitzberg and Ambrose Little) [Usability Resources]