To connect your Office 365 Calendar to Drift, you'll first want to navigate to the calendar settings by clicking on the Meetings tab.

Note: Drift can only connect directly with Office 365. Exchange, Exchange Online and Hybrid Exchange calendars will not connect. 

If it's your first time here, simply click the Connect Calendar button seen in the screen shot above.

Next, select the option for Office 365 and continue through the workflow to connect your calendar.