Fossil fuels, such as coal, oil, and natural gas, are easily turned into energy through combustion. They have high energy density and can be burned to produce heat, which can then be converted into various forms of energy, including electricity. However, it is important to note that while fossil fuels are easily turned into energy, they are not considered clean energy sources due to the significant environmental impact associated with their extraction, production, and combustion. Additionally, fossil fuels are not an infinite source of energy as they are non-renewable and will eventually deplete.