The Secretary of State (I am assuming you mean of the United States) is our nation's chief diplomat. Basically, he/she is responsible for implementing foreign policy on behalf of the President of the United States. He/she also oversees all embassies, US Foreign Service and USAID.
The designation of "Secretary of State" is most commonly used for the most important member of the Cabinet of the President of USA. There is no fixed portfolio for the secretary of state as per constitution. The President decides on many of the duties to be performed by the secretary of state from time to time. The main function of the secretary of state, among others, may include the following:
- Principal adviser to the president on foreign affairs.
- Negotiating with foreign representatives.
- Instructing U.S. embassies abroad.
- Custody and use of Great Seal of the United States.
- Performing White House protocol functions.