Black is hot, white is neutral, green is ground- usually a device ground, bare copper will be the system ground. The connect points (on newer items) are usually color coded as well. When wiring a receptacle, for example, black goes to the brass, white to the silver, and green or copper (or both) to the green separate screw lug. That connects the system ground to the round ground slot on the receptacle just below the two vertical slots.
Wiring a plug on an appliance like a vacuum cleaner, black goes to the brass, white to the silver, and green to the green separate screw lug. That will connect the ground line from the appliance to the round ground prong on the plug, so when it's plugged in everything lines up properly.
Often, small things like toasters or coffeemakers don't have a separate ground. There is so much plastic in the construction, they are considered self-insulated. Not sure if I like that. Anything designed by humans can screw up.
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element