When wiring a wall outlet the neutral (white) wire should connect to the white or silver metal screw. The hot (black) wire should connector to the brass colored screw. The green screw obviously ties to the bare ground wire. There is a tab between each of the screws of similar color. This allows you to put the top and bottom receptacles on separate circuits or to put one receptacle on a switch. This tab can be removed with some needle-nose pliers if needed. You normally leave the tab in place so that both outlets are powered once you connect to either of the screws.