In this window, you can see for all configured banks the last date, when account statements and advices were retrieved. Normally, you do not need to enter anything here. However, if account statements are missing, you can set a date of the past. If you then select Retrieve account statements from the Actions menu, account statements are requested from this date at the bank. The same works for advices accordingly.
A blank field means that no account statements or advices have been retrieved yet for this bank.
This function is also available in the bank properties. Please refer to the chapter Jobs - Bank properties - Account statements. It makes no difference whether you perform the function here or there.