After you click the File tab, you can see the Microsoft Office Backstage view. The Office Backstage view is where you manage your files and the data about them — creating, saving, printing, inspecting for hidden metadata or personal information, and setting options. In short, it is everything that you do to a file that you don't do in the file.
The File tab replaces the Microsoft Office Button and File menu used in early releases of Microsoft Office.
Where is the File tab located?
The File tab is a colored tab, for example, a blue tab in Word, located in the upper-left corner of Microsoft Office programs.
What do I see when I click the File tab?
When you click the File tab, you see many of the same basic commands that you saw when you clicked the Microsoft Office Button or on the File menu in earlier releases of Microsoft Office, such as Open, Save, and Print.
Show me Backstage view
You can watch a video that shows you more about Backstage view at Video: What and where is Backstage view.