The function or the purpose of the central banks around the world is to ensure that a country is financially stable and economically sovereign. For example, The Reserve Bank of India is the central bank of India. The function of RBI is to support and direct the monetary policies, issue and manage various kinds of currencies, control credit, manage the foreign exchange and is also acts as a bank to other banks and is the personal bank for the Government of India.
Hope this helps you.
Image Courtesy: Google
Also Read- What is the bhartiya reserve Bank note mudra private limited?