Ribbon is a command bar that organizes important features into tab and button at the top portion of the screen, which was introduced in NAV 2009's Role Tailored Client (RTC). It is now available in both NAV 2009 and NAV 2013 RTC.
Ribbon make the important features more discoverable and easier to access. This has makes NAV more user friendly and easier to learn. However, the Ribbon takes up a significant amount of screen space, which in effect will reduce the working space on the screen.
Luckily, NAV has the option for users to show or hide the Ribbon. When you need more working space, simply press CTRL + F1 to hide the Ribbon. When you need to Ribbon again, simply press CTRL + F1 again to bring back the Ribbon.