Name the three energy roles of organisms in an ecosystem. How does each type of organism obtain energy?

I believe the types of organism classifications you are looking for are producers, consumers, and decomposers.

Producers are autotrophs such as plants, and some types of protists. These are the organisms that are capable of taking the light energy of the sun and transforming/storing it as chemical energy in the form of sugars. That is, they perform photosynthesis (carbon dioxide + water ---> sugars and oxygen). Without this group, the rest of the living things on earth would quickly die out. There are some producers that are chemotrophs--these utilize the energy from geothermal features such as the vents in the deep ocean.

Consumers are heterotrophs--organisms such as animals and some protists, that consume the stored energy from plants or from other animals. Even if total carnivores (animals that only eat other animals) they are still dependent, ultimately, on producers, as their prey eat the producers.

Decomposers such as fungi and bacteria also utilize the energy contained in dead plant and animal matter. They are not classified as consumers, however, as they do not "eat" the organic matter; instead, they chemically alter the dead matter and absorb the energy.