When you turn on auditing, activity in your organization is recorded and available to view in the Office 365 activity report. ...

When you turn on auditing, activity in your organization is recorded and available to view in the Office 365 activity report. This report contains records for user and admin activity in SharePoint Online, OneDrive for Business, and Azure Active Directory. You can use this report to look for specific activity, such as which files have been recently shared or which users have signed into Office 365.