Nothing. The battery is sealed an no harm will be done.
Jump the car from another car battery or hook a charger to the battery.
You can get a new battery, you can jump start the car with jumper cables and another car with a charged battery. You can also put a battery charger on your battery to give it a charge.
If the battery has more cranking amps than the recommended battery and will fit into the battery carrier box the answer is yes.
Is there power to the starter "S" terminal? What car?
Disconnect negative cable first from old battery and connect it last when installing new battery.
No, it will do nothing
yes
No
The one that the car's manual specifies. This will be different for every car.
take the car to a repair shop and have them put a battery tester on it. it may be the alternator or the battery the tester will tell
What brand is the car?