The app launcher enables you to navigate across your services and apps in Office 365. Did you know that you can also pin up to three apps in your navigation bar? This makes those apps available instantly, from any Office 365 page or app.
To pin an app to the navigation bar
Choose the app launcher at the top of the page to open it, and then decide which app you want to pin to your navigation bar.
Click (or tap) the ellipsis (...) on the tile, and then choose Pin to nav bar.
The app is pinned to the navigation bar, at the top of the screen.