Here you have to select the name of the report procedure that will print your windows. Since this is a global setup, all your "PrintWindow" controls will call this report unless override locally.
Warning: If you don't select a report here, your program will successfully compile anyway, but nothing is going to happen when you press the "Print" button.
The report you select here should be the one referred in Report Design (Local Extension).
You may use several reports to use different print options (for example, one report for portrait and another for landscape). Name here the most often called report, then you override locally only the windows that won't use this report.