To administrate is to manage or run something. People who administrate are in charge.
An administrator is someone in charge of something, like the president of a college. To administrate is to run something, the way a CEO runs a company. Administrating means making major decisions, hiring and firing people, and taking credit and blame for what a business or organization does. It can help you remember what this word means if you remember that the current members of the executive branch of the U.S. are called the administration.