Supreme is used in the title of a person or an official group to indicate that they are at the highest level in a particular organization or system.
MacArthur was Supreme Commander for the allied powers in the Pacific.
麦克阿瑟是太平洋盟军的最高司令。
the Supreme Court.
最高法院。
You use supreme to emphasize that a quality or thing is very great.
Her approval was of supreme importance.
她的认可是极其重要的。