ME2N lists purchase-order items. Selection determines the records in the report, while the ALV layout determines which columns you can inspect. Purchase Order identifies the header and Item identifies the line. Keep both when one PO contains several materials, or a later reconciliation can collapse distinct items into one record.
The Amount column in this training report is ordered quantity times PO price. It is a purchasing commitment, not proof of an invoice or a payment. Open Quantity is ordered less received quantity and helps you find incomplete deliveries. These exercises use vendor, material and quantity filters to answer specific purchasing requests. An empty result can be correct when no record matches the selection.