A department is a group of people who work together to do something. Science is the study of the natural world. So, a department of science is a group of people who work together to study the natural world.
The Department of Science is the government department responsible for science in Australia. It is responsible for funding research in areas such as climate change, energy, agriculture, and health. The Department also provides policy advice to the government on science-related issues. To explain what the Department of Science does, we can say: The Department of Science is responsible for funding research in areas such as climate change, energy, agriculture, and health. It also provides policy advice to the government on science-related issues.