What comes down the street from the power company depends on the neighborhood and the sort of draw that they expect - but essentially you will have high voltage wiring, typically 400-1000V, and 1-3 phases, none of which really matters to normal users since they never get near it.
Our main distribution system is based on 3-phase power, with three phases that are 60* apart. The voltage varies depending where in the distribution network you look at, with main trunk lines being very high voltages, getting stepped down to lower values as you get closer to the customers.
High power demand industrial type users will get all three phases, usually 220V or for the real heavy hitters, 440V per phase, which gets hooked up to industrial power tools like milling machines, and manufacturing equipment. Then there will also be systems to break everything down and distribute it to the usual 110V outlets and lighting, etc. that get used for everything else.
In single family neighborhoods there will be transformers every couple of houses that look like garbage-cans hanging on the poles. In apartment houses and so on, the high voltage wiring will go into the building and power a transformer and distribution wiring in a closet somewhere, but same basic deal.
The transformer takes the high voltage and chops it to 220V. It is in effect a 'center-tap' style transformer, so you have 220V across the outside terminals and 110V between either outside terminal and the center tap (which is tied to ground). So you end up with the two 110V 'hot' lines (AKA 'legs') and the center-tap neutral... The 110V lines are 180* out of phase with each other, but on a larger scale are considered to be a single phase of the main 3-phase power system.
So the standard outlet in the US is 110V, with a wide (lengthwise) flat slot hole, connected to white wire, that is 'neutral', a slightly narrower flat slot connected to ONE of the two black 110V hot wires, and a small round hole that connects to the Green 'safety ground' wiring. (colors specified by electrical code) The Neutral and safety ground wires are supposed to be tied together at the service entrance (main electrical panel) and nowhere else.
There is hopefully NEVER any current flowing on the green safety wiring, it is there only to provide a safe path to ground if something shorts. (Any exposed metal bits are supposed to be connected to the safety ground, so a hot wire connecting improperly will short to ground and blow the fuse...)
As Lenny mentioned, heavy draw appliances (that almost by definition are non-portable) will have dedicated 220V outlets that will (at a minimum) have the two 110V hots, and a safety ground, but no neutral, Some appliances may also have 110V bits as well, like the clock on the electric stove, and for those you will have a neutral wire that is only connected to the 110V bits.
The distribution of where the two 110V lines go in a house is moderately complex, and dictated by electrical code, but basically amounts to trying to keep the load on the two 'legs' as equal as possible, and also making it difficult to have electrical equipment that is connected to different legs sitting next to each other...
Burgerman wrote:How do they get 110 from single phase 220V? Or is the 220 actually 2 phases? And 110v is N plus a phase? Or they would need twice as many cables into the house.
It should be simple then to run a set of cables and breakers for EU or UK style sockets at 240V for big tools, heaters, power supplies, etc. Makes you wonder why they would want 110 as well. Just gives more room for errors...