It's possible that the outlet is on a switch, and either one half of the outlet is switched or the whole thing. The extra two pair of wires probably feed the NEXT outlet.
You use a known ground and check them for voltage. You can use an extension cord to reach from a ground to the wires you are testing. You are not putting it in an outlet, just to connect you to a ground.
Black, white, and copper.
the bare copper is always a ground
The ground wires are twisted together and then connected to the GFCI ground. The black and white wires may also be twisted together and then using a jumper wire connected to the GFCI. Hard to say without seeing exactly how it is wired.
wire nut the three whites together with a fourth wire going to the outlet same for the black
In North America (Canada, United States, Mexico) a household 110V-120V outlet has three wires: hot, neutral and earth ground. If the outlet is mounted in a grounded metal box, the third wire (earth ground) may not be present, since the connection to ground occurs through the metal outlet housing and possibly metallic conduit that routes the wires from the circuit breaker panel to the outlet. Where metallic conduit isn't used, the earth ground wire may be connected to the metal box, and the earth ground pin of the outlet is connected by securing to the box with screws.
If the wiring system into which you are installing an outlet has no ground available, use an ungrounded outlet. In an ungrounded system, an outlet with a ground contact would allow the outlet user to mistakenly, and perhaps dangerously, assume that a ground was present. A suitable ground may be available as a ground wire accompanying the hot and neutral wires in the cable, or a ground may be available via conductive conduit and a metal outlet box. In any case, use a tester to confirm the integrity of the assumed ground. A voltage test from the hot wire to the ground should show the same voltage as between hot and neutral (the black and white wires respectively). If you are replacing an ungrounded outlet, you need not assume there is no ground present. You may find, in the box, ground wires that were not connected to the outlet. You may come across grounded outlets that have no ground wire attached because they rely on grounding via the mounting screws through the outlet ears to the metal box. This is a less reliable grounding method. It is better to buy a ground-wire "pigtail," fasten the wire directly to a hole in the metal box with the supplied screw, and attach the other end of the ground wire to the outlet via the outlet's ground screw.
hot wires are black, white wires are ground
The supply black (Hot) wire from the outlet feeds each switch (attach two pigtail black wires from the outlet black wire). The other side of each switch goes to the load. The three white wires (Neutral) get connected together (1 from outlet and 1 from each load). The three bare wires (ground) also are connected together.
The fan is probably a 115 VAC single phase fan and the outlet is probably a 230 VAC "two phase" outlet. The fan would then have the following wires: hot (black), neutral (white), and ground (green). The outlet would then have the following wires: hot #1 (black), hot #2 (red), neutral (white), and ground (green). Pick either of the two hot wires on the outlet and connect the hot wire of the fan to that (ignore the other hot wire on the outlet) and connect the neutral to neutral and ground to ground. If the wire colors are not as I described above you may have something else (e.g. 3-phase) and that would be wired differently, but those systems are usually used only in industrial settings not the home.
connect your black wires to the right side of outlet on the gold screws white wires on the left side silver screws and bare copper wire to green ground screw.