Coal

Coal is a readily combustible black or brownish-black sedimentary rock. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. It is composed primarily of carbon along with variable quantities of other elements, chiefly sulfur, hydrogen, oxygen and nitrogen.

How it works
The process of converting coal into electricity has multiple steps and is similar to the process used to convert oil and natural gas into electricity:

A machine called a pulverizer grinds the coal into a fine powder.
The coal powder mixes with hot air, which helps the coal burn more efficiently, and the mixture moves to the furnace.
The burning coal heats water in a boiler, creating steam.
Steam released from the boiler powers an engine called a turbine, transforming heat energy from burning coal into mechanical energy that spins the turbine engine.
The spinning turbine is used to power a generator, a machine that turns mechanical energy into electric energy. This happens when magnets inside a copper coil in the generator spin.
A condenser cools the steam moving through the turbine. As the steam is condensed, it turns back into water.
The water returns to the boiler, and the cycle begins again

(Source: http://www.teachcoal.org/aboutcoal/articles/coalconvert.html)

Status and Contribution
In 2006, the total production of the global coal industry stood at 6,152 million tons (MT).According to the British Petroleum statistical survey, the market share of the prominent coal producers of the world in 2006 was pegged at:
China - 38.4%
USA - 17%
India - 7.2%
Australia - 6%
Russia - 5%

Advantages of Coal

Easily combustible, and produces high energy upon combustion, helping in locomotion and in the generation of electricity and various other forms of energy
Widely and easily distributed all over the world
Comparatively inexpensive due to large reserves and easy accessibility
A coal-based power station can be built almost anywhere, so long as you can get large quantities of fuel to it.

Disadvantages of Coal

Non-renewable and fast depleting;
Burning coal releases carbon dioxide, a powerful greenhouse gas that had been stored in the earth for millions of years, contributing to global warming.
Coal leaves behind harmful by-products upon combustion, thereby causing a lot of pollution
Mining and burning of coal pollutes the environment, causes acid rain and ruins all living creature's lungs.
Coal reserves are finite; they will eventually run out.

Important Facts

The global coal market grew by 18.9% in 2007 to reach a value of $312 billion.
In 2012, the global coal market is forecast to have a value of $355.9 billion, an increase of 14% since 2007.
Nine out of every 10 tons of coal mined in the United States today is used to generate electricity, and more than half of the electricity used in this country is coal-generated electricity.

See the following sections in non renewable energy

See also

The World Coal Institute

Brief summary and related resources on coal

An interesting article on coal at a glance 2006