Coronations are often centuries-old ceremonies with a great deal of formal and solem traditions. Usually the climax of the coronation ceremony is the monarch's recital of a special oath, followed by a religous leader placing a special crown on the monarch's head.
A monarch does not necessarily have to be properly crowned in order to execute the duties of his office, however. For example, King Edward VIII of the United Kingdom never had a coronation, yet was unquestionably the king of the United Kingdom during his brief reign.