How is the energy source of coal obtained?

Answer 1

as in where coal comes from its the remains of plant life which has been fossilised and partially decomposed to form coal, high in carbon.
how the energy comes from coal, well thats due to the oxidation of carbon in an exothermal (energy releasing) reaction which occurs during the burning process

Answer 2

Energy of coal is stored solar energy. Coal was made of plants that used solar energy to absorb CO2 and solar energy to make wood like stuff that became coal over time. The energy source is the sun and the process is growing plants and storing the product plants produce.