Here you enter the payment date (due date) for those invoices that are being confirmed. You can enter "from" one due date in the upper field "to" another due date in the lower field, if you want to report payments made during a whole week etc. Today's date is entered by default in the lower field.
If you perform confirmation every day, it may be more convenient to enter yesterday's date in the lower field, in order to only show those invoices that were past due yesterday or earlier.