Grounding is done to help steady the power level, bleed off lightning strikes, and provide a general level of safety. Grounds originally were often metal stakes driven into the earth, or metal plates buried in the ground, connected to the building fuse box with heavy buss bars. Sometimes the cold water pipe was used. Grounding today is generally done at the power company owned utility pole and other parts of the power system. For any proper power protection scheme, a good solid earth ground is a critical component of the system.
Bad grounds can cause power fluctuations among other problems.
Voltage Voltage is simply a measurable component of electricity that is analogous to how much pressure is in a waterpipe. In the United States, the voltage level at a standard pronged outlet usually ranges between 110 to 120. In a house, and in many commercial buildings, the voltage level brought in from the street is twice this amount, or 220-240v. It is brought in on three wires, basically a black Hot pair that share a common Neutral wire, this wire is connected to Ground. Each pair is split off at the fusebox, and the electrician wiring the building usually attempts to evenly divide the circuits in the building so that half are on one pair, and the other half are on the other.