To understand what is Header Project and Item Project, please refer picture below:
To understand where to get this two column from report designer.
1. Now hold the mouse-left key, to drag the either the item project or the header project's "Description" field, from the Field List panel on left to the design area.
2. Click "Preview" tab to preview the report. You can find the "Preview" button at the bottom of the report design area.
3. Click the "Save" button on top-left to save the new report format to database.