Connect the ground wire from the light fixture to the ground wire in the ceiling box.
Yes. Connect Black to Black, White to White and bare ground wires together.
Connect the ground wire to the metal box.
Connect the ground wire in wall to the base of fixture
If you mean 2 bare copper wires those are the ground wires. Tie them together and then connect the light fixture ground wire which will be green or bare copper to those ground wires.
I always connect the ground wire to the box. However, if there is no real ground wire running back to the panel it really does you no good. The NEC requires that you rewire the circuit with the proper conductors. Remember that the ground is for your protection. Without a proper ground, you run the risk of injury or death if the fixture wiring fails.
If you are referring to a porcelain or plastic ceiling light fixture most do not have a place to connect the ground wire. You cannot ground these type fixtures. Just connect the ground wire to the mounting crossbar and forget about connecting it to the light itself. It is on the ceiling and will never be touched unless you change the bulb and then you will have the switch in the off position. It is perfectly safe.
it will explode
The light is wired the same as any voltage fixture. Bring the source voltage to the fixture and connect it to the two fixture wires. If you want to control the off-on of the fixture take the source voltage to a switch first and then out of the switch to the light fixture.
Connect black to black and white to white from the switch. Your old fixture may have had wiring for multiple bulbs so they could be switched separately.
To control a light with a switch, the switch has to be connected in series with the light fixture.
In USA an AC light fixture isn't polarized, so color-matching wires is not required.