Need to find if a user viewed a specific document or purged an item from their mailbox? If so, you can use the Office 365 Security & Compliance Center to search the unified audit log to view user and administrator activity in your Office 365 organization. Why a unified audit log? Because you can search for the following types of user and admin activity in Office 365:
User activity in SharePoint Online and OneDrive for Business
User activity in Exchange Online (Exchange mailbox audit logging)
IMPORTANT: Mailbox audit logging must be turned on for each user mailbox before user activity in Exchange Online will be logged.
Admin activity in SharePoint Online
Admin activity in Azure Active Directory (the directory service for Office 365)
Admin activity in Exchange Online (Exchange admin audit logging)
User and admin activity in Sway
User and admin activity in Power BI for Office 365
User and admin activity in Microsoft Teams
User and admin activity in Yammer
NOTE: Activity logging for Yammer might not be available yet to applicable customers.