Each cabinet-level agencies are headed by a single person with a “secretary” title. These cabinet secretaries are appointed by the President and their appointments can only be formally confirmed when the Senate approves their position. Once approved, these secretaries will work under the executive branch of the government and they should report directly to the President.
All appointed cabinet secretaries work at the pleasure of the president. This means that the president can demand the resignation of any cabinet secretaries for whatever reason he may serve him best. On the other hand, there are some who are exempted from this rule, such as those that are serving on a fixed term basis, like the Director of the FBI.