Unlike the Federal Bureau of Investigation (FBI), which is a domestic security service, CIA has no law enforcement function and is mainly focused on overseas intelligence gathering, with only limited domestic collection. Though it is not the only U.S. government agency specializing in HUMINT, CIA serves as the national manager for coordination and deconfliction of HUMINT activities across the entire intelligence community. Moreover, CIA is the only agency authorized by law to carry out and oversee covert action on behalf of the President, unless the President determines that another agency is better suited for carrying out such action. It can, for example, exert foreign political influence through its tactical divisions, such as the Special Activities Division. 

The Executive Office also supports the U.S. military by providing it with information it gathers, receiving information from military intelligence organizations, and cooperating on field activities. The Executive Director is in charge of the day to day operation of the CIA, and each branch of the service has its own Director. The Associate Director of military affairs, a senior military officer, manages the relationship between the CIA and the Unified Combatant Commands, who produce regional/operational intelligence and consume national intelligence.
Where do they mostly work?
mainly focused on overseas