GFCI outlet with 6 wires?

You need to find which set of wires is the feed 1st. Turn off breaker for that circuit disconnect wires . Then turn breaker back on . Which black wire is hot ? Remember which black wire has power. Then shut off breaker again . The black wire that is hot gets connected to your line voltage connection side ( Gold screw on outlet ) the white wire goes to the other line voltage side ( Silver screw ) . The other black and white wire gets connected to the load side of the GFI . If the screws are all the same color for some reason . Remember the longer slot is always the neutral or white wire . The smaller slot is the black or hot wire . Ground to the green screw .Turn breaker back on and test .