Where did the fossil fuels get there energy?

Answer 1

Ultimately, all energy only comes from the Sun. This is how the energy is transferred: Sun>plants>animals. Therefore, fossil fuels obtain their energy from plants itself and animals when they've consumed plants.

Answer 2

Fossil fuels get their energy from the sun. Millions of years ago, plants and organisms absorbed sunlight through photosynthesis, converted it into chemical energy, and stored it in their tissues. When these plants and organisms died and got buried underground, the stored chemical energy became fossil fuels over time.