Focused Inbox helps you focus on the emails that matter most to you. It 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. You’ll be informed about email flowing to Other, and you can switch between tabs at any time to take a quick look.
Please visit Turn off Focused Inbox for detailed instructions for turning focus off.
Check out Microsoft's FAQs for Office 365 (https://support.office.com/). Microsoft also has some great training videos you can watch to become familiar with using Office 365 applications. Please visit the Office Training Center.