How to create Audit Log reports in SharePoint online /office 365?

Auditing can be configured for a site collection, a list or library, or based on a content type as part of an organizations information management policy.The audit log reports can be accessed from Audit log reports under site collection administrator. Below are the events captured in Office 365 are

Content Activity Reports

Content viewing

This report shows all events where a user viewed content in this site.

Content modifications

This report shows all events that modified content in this site.

Deletion

This report shows all events that caused content in this site to be deleted or restored from the Recycle Bin.

Content type and list modifications

This report shows all events that modified content types and lists in this site.

Information Management Policy Reports

Policy modifications

This report shows all events related to the creation and use of information management policies on content in this site.

Expiration and Disposition

This report shows all events related to the expiration and disposition of content in this site.

Security And Site Settings Reports

Auditing settings

This report shows all events that change the auditing settings of Microsoft SharePoint Foundation.

Security settings

This report shows all events that change the security configuration of Microsoft SharePoint Foundation.

Custom Reports

Run a custom report -Manually specify the filters for your Audit Report. The filters available for manual reports in Office 365 are

Opening or downloading documents, viewing items in lists, or viewing item properties
Editing items
Checking out or checking in items
Moving or copying items to another location in the site
Deleting or restoring items
Editing content types and columns
Searching site content
Editing users and permissions
Editing auditing settings and deleting audit log events
Workflow events
Custom events