A more thorough explanation:

The State Department, also known as the Department of State, is a part of the United States government that helps the President with foreign policy. The Secretary of State is the head of the department and negotiates treaties and agreements with other countries. The department also represents the United States at international meetings and conferences.

For example, if the President wants to make a deal with another country, the State Department will help negotiate the terms of the agreement. They also speak for the United States at the United Nations and other international organizations.

The State Department is made up of six bureaus that handle foreign affairs for different regions of the world, such as African Affairs and European Affairs.