1. Photosynthesis: Plants, algae, and some bacteria use sunlight, water, and carbon dioxide to create their own food (sugars) and oxygen. This process is called photosynthesis. It's the fundamental way that energy from the sun enters the food chain.

2. Organic Matter Accumulation: Over millions of years, vast amounts of these photosynthetic organisms died and were buried under sediment (like mud, sand, and silt) in swamps and bogs. The lack of oxygen prevented complete decomposition, allowing the organic matter to accumulate.

3. Transformation: The organic matter underwent a series of chemical and physical transformations due to pressure, heat, and the action of bacteria. This process converted the dead plant material into peat, a partially decayed organic matter.

4. Coal Formation: As more sediment piled on top of the peat, increasing pressure and heat further transformed it into coal. The type of coal produced depends on the degree of transformation.

In essence, coal is fossilized sunlight. It's the stored energy of ancient plants that used photosynthesis to capture sunlight millions of years ago.