Office for Mac has a menu bar that does not exist in Office for Windows. It is at the top of the window. You will find the File menu on the menu bar.
The features and functionality in the Windows version are almost all included in the Mac version, but they may be in different places or have different names.
If you tell us what you're looking for in particular, we can point you to the location in the Mac interface. A lot of the Backstage content is in New From Template on the File menu.