The Ribbon is the display you see at the top of the program's window. It is your primary interface with the program. It allows you to access most of the commands available to you in Word. The Ribbon is composed of three parts: Tabs, Groups and Commands.
The following is the Word 2013 Ribbon:
Note that the FILE menu is not the same as a tab. The FILE menu takes you to the Backstage view, where you manage your Office information, as well as what you are working on.
The tabs of the Ribbon organize the commands into groups.
For example, here is INSERT tab in Excel. You can see that it is composed of groups and the commands within the groups.
To further organize the many commands available in Microsoft Word, commands are organized in groups on each tab. Each group contains three or more related commands.
The following is the Proofing group in Excel, which is located on the REVIEW tab. You can see it contains the commands: Spelling, Research, and Thesaurus.
In some groups, you will see a button in the lower-right corner, next to the group name. This is the Dialog Box Launcher. Opening the group's dialog box will give you access to additional commands associated with that group: