The transformer provides the electricity at the right voltage for the house.
In all countries it makes sense for all the houses to be fed with the same voltage, which simplifies the market for electrical applicances. Most countries use a standard voltage in the range 100-125 v or 220-240 v.
The electrical energy has to be transmitted over long distances at a higher voltage unless you want to live next to a generator, so the transformer changes the voltage from a higher voltage like 6600 v to the correct voltage for the house, e.g. 230 v.
It goes through a step up transformer then a step down transformer then into your home. It goes through wires.
Your home will have single phase power coming to it.
In home electronics, it changes 120volt AC electricity into (usually) 12volt or less DC electricity for use in small electronic items that do not need high voltage to operate.
It comes along wires in the street that take the power from a transformer. The transformer is fed by wires working at a higher voltage, and there are usually several transformer stages at different voltage levels leading back to the nearest power plant.
Cybertron
For any electricity supply there has to be a pair of wires to carry the electric current. One of the wires is connected to earth at the transformer where the power comes from. That one is called the neutral. They can't both be grounded so only one of them is, and that prevents a buildup of static electricity.
A transformer changes the electricity from one voltage to another, which allows a high voltage power line to be converted down to a voltage suitable for home usage.
Yes you could use a 20 kva transformer in a home. Stymied as to why it would be done though. You would need at least a 100 amp service to the home to energize the transformer. Primary side of the transformer would draw 83 amps at 240 volts. If the question was to supply the home, again yes. It would be 100 amp service equipment that the transformer would feed into.
A power plant produces electricity (electromagnetic energy) which is delivered to a user's home. There is no transformation as electric power is created at the plant, delivered via the power grid and used in the home.
fly-back transformer.
A power transformer is used to provide power (to your home, for example), an instrument transformer is used to measure voltage or current (for metering, for example).
a step down transformer is used to lower the voltage from the powerlines into your home. a common slang term for this type of transformer is a pole pig.