Black is used for the "Hot" wire.
White is used for the "Neutral" wire.
Green (or bare wire with no insulation) is used for the "Ground" wire.
IF YOU ARE NOT ALREADY SURE YOU CAN DO SOME ELECTRICAL WORK
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
If you do any such work yourself, always turn off the power at the breaker box/fuse panel BEFORE you attempt to do any work AND always use a meter or voltage indicator to insure the circuit is, in fact, de-energized.