The Debitor & kreditor tab shows what customers owe you (receivables) and what you owe suppliers (payables) — with ageing.
Open balances per customer and per supplier.
Ageing (how old the entries are).
Overdue amounts.
Click into a customer or supplier to see the underlying vouchers (Receivable vouchers / Payable vouchers).
Use the department filter to narrow down.
"Posted" means figures as they are recorded in the accounts.