When the audit functionally is enabled it will automatically log events and activities that are done on your content. The Content could be documents, records and other items, such as Task list and calendars. The Reporting Site Collection feature must be activated in order to see any audit reports.
Also you can check out:
Administrator access to configure auditing. We enable auditing on these levels: Site Collection, library/list, folder and content type.
1. Go to Site Collection Settings. See in fig
2. Under Site Settings -> Site Collection Administration -> Site Collection audit settings. See in fig.
3. Under the Document and Items section you can enable the events you would like to audit. See in fig.
4. On the same page you also have the option to enable audit logging for Lists, Libraries and Sites. See in fig
1. Go to library Settings -> Permission and Management -> Information management policy settings. See in fig
2. Under the Content Type Policies Select Document content type. See in fig
3. Now Scroll down to Auditing where you will be able to choose the events you want to add to the audit log. See in fig