Fossil fuel's are made of organic materials this means that they come from

This means that organic material comes from carbon-based compounds, originally derived from living organisms. The majority are a combination of hydrogen, carbon, nitrogen and oxygen and can be divided in three groups: The organic material coming from plant material, the organic materials that have an animal origin and the organic material that comes from oils.

Fossil fuels are formed by a natural processes, which is the decomposition of buried dead organisms.

Fossil fuels are made of organic matter. This means things like trees and plant matter. Fossil fuels are composed of primarily three groups, that is natural gases, coal and oil. Coal for example was formed over millions of years. As ancient trees would decay that plant matter would sink into swamps. Then over time and due to pressure from other materials the plant matter would turn into coal.