In OrCAD and other similar systems, power and ground layers are treated as planes. Thery are displayed inverted for drawing speedup, so pads in those layers are holes in copper plane. If you need only one ground and one power, use power and ground plane. If you need multiple power lines (3.3V, 5V...) and/or segmented or splitted ground planes, use IN1 etc. inner layers, because you cannot easily route tracks in plane layers. In inner layers use copper pour for planes. All this is described in user guide.
Regards
BGAman.