An electric generator has two parts: the rotor, (which rotates!), and the stator, which stays still inside the rotor and is covered with copper wire. The rotor has a powerful magnet in it. Electricity is created when the rotor moves around the stator, and the magnetic field from the rotor creates an electrical charge inside the copper wire. This charge is collected and sent out as electricity.
The way a generator works is that some form of energy must be used to create the motion which turns the rotor. In a portable generator such as you might use in an area with no electricity, a gasoline-powered motor is used to turn the rotor. With Thermo-electricity, steam power is used to turn a steam turbine. The turbine has blades inside a chamber. Steam under pressure is forced into the chamber. The pressurised steam pushes against the blades of the turbine which causes the blades to turn. This turns a shaft which is connected to the generator.
The sources of energy for creating thermo-electric power can include burning coal, oil, and using nuclear energy to create heat. All these sources of energy are from non-renewable resources and some types, particularly burning coal, can cause pollution which can damage the environment. Nuclear energy is probably the most efficient way of creating thermo-electricity. Ontario has several nuclear power plants and some of the electricity that comes to your home may come from this source.
Hydro-electricity uses the power of falling or flowing water to generate electricity. This water comes from rivers and even waterfalls. Niagara Falls has a hydro-electric power plant at the base of one of the falls. The advantage to using water as a source of energy is that it is renewable. Once a dam is built to create a flow of water, that water source will always be there to provide power. It doesn't get used up and it doesn't cause pollution.