The Office 365 app launcher is a menu of Office 365 apps and services, depicted in tiles. The app launcher will provide you quick access to your Office 365 apps. You can access the app launcher via its icon in the top-left of Outlook on the web:
Important: Microsoft continues to make updates to Outlook on the web to simplify working with your apps and online documents. As part of this update, the app launcher will get a face lift.
The Office 365 navigation bar is the bar that runs along the top of Outlook on the web. The app launcher is contained here, as well as other options.