How is energy passed through an ecosystem? What role does the sun play? What role does the water play? How are decomposers involved?

I can answer your first question. Energy is transferred between organisms in food webs from producers to consumers. The energy is used by organisms to carry out complex tasks. The vast majority of energy that exists in food webs originates from the sun and is converted (transformed) into chemical energy by the process of photosynthesis in plants.