Custom Reports can be added for an event by clicking 'Events' from the main menu, 'Events' again, clicking on the name of the event, 'Reports', 'Custom Reports', then and 'Add Report'.
You can give the report a name, select whether to include Attendees data or Orders data, choose which columns to be included and use the filters before saving the report.
The new report will then be available on the Custom Reports page. To run reports you've created, click 'Run'. Once the report has been generated you can view the report details and click 'Export to CSV' to export the report to your computer.