Adapted from Office.com:
Focused Inbox separates your inbox into two tabs—Focused and Other. Your most important emails are on the Focused tab while the rest remain easily accessible—but out of the way—on the Other tab.
Turn Focused Inbox on/off
In Outlook 2016, select the View tab.
Click to select Show Focused Inbox to turn it on. Click again to de-select it and turn it off.
The Focused and Other tabs will appear at the top of your mailbox if "Show Focused Inbox" is turned on. You’ll be informed about email flowing to Other, and you can switch between tabs any time to take a quick look.
Change how your messages get organized
From your inbox, select the Focused or Other tab, and then right-click the message you want to move.
If moving from Focused to Other, choose Move to Other if you want only the selected message moved. Choose Always Move to Other if you want all future messages from the sender to be delivered to the Other tab.
If moving from Other to Focused, choose Move to Focused if you want only the selected message moved. Choose Always Move to Focused if you want all future messages from the sender to be delivered to the Focused tab.