You should now understand that:
Ecology is a scientific approach to the study of the biosphere.
Ecosystems are created by the interrelationships between living organisms and the physical environments they inhabit (land, water, air). Ecosystems require a source of energy to make them work and for most, although not all, this is light from the sun.
To study ecosystems we have to start to identify the components involved and the interrelationships between them. We can list the living organisms by identifying the species involved.
Food chains and food webs are a way of mapping one type of interrelationship between the organisms in an ecosystem.
Human beings are part of ecosystems, as well as manipulators of ecosystems. As such we are dependent on, as well as responsible for, the ecological health of the ecosystems we inhabit.