Ecology is the study of interactions among and between organisms
(plants, animals, humans) and their environment. It combines the sciences of botany (plants), zoology (animals), and other disciplines like hydrology, geography, and ecosystem processes (like nutrient processes). Biodiversity refers to the variety of plants, animals and ecosystems sharing our world, and is part of ecology.
Ecology looks at how everything in the world is related to one another, including humans. How humans behave in their environment impacts how organisms continue to exist and carry out their interactions within their environment which in turn impacts humans. For example, an action by humans could improve how bees pollinate flowers which could improve our food production and in turn feed more people.
Ecology matters tremendously.