Nick Fury, Maria Hill, and Victoria Hand have not been given much background in the Marvel Cinematic Universe. Each of the characters has an extensive dossier in the canon Marvel Earth-616. Unfortunately, their profiles are quite divergent, so for the sake of reference, I will only use the Marvel Cinematic Universe notations.
Nick Fury is the Director of S.H.I.E.L.D. He is the top dog in the overall organization and the tactical leader of any S.H.I.E.L.D. op he wants to control. Fury's clearance allows him access to almost any government level military secrets and technology and he answers to a mysterious council of world leaders whose identities remain unknown.
The Marvel Cinematic Wiki is the source of all of the following references:
Nicholas "Nick" Fury is an officer of the US Army and espionage veteran of the Cold War who now leads S.H.I.E.L.D., a covert international peacekeeping organization which operates as humanity's first line of defense against Earth's most dangerous enemies. His job as the Director of S.H.I.E.L.D. led him to all sorts of unusual adventures, including dealing with superhumans and extraterrestrials.
Fury's extraordinary military and espionage skills won him the position of the executive head of the Strategic Homeland Intervention, Enforcement and Logistics Division, an international peacekeeping organization. Fury is also credited as a possible co-creator/designer of the Avengers Initiative as well as the special operations commander.
Maria Hill is the Deputy Director and answers directly to Nick Fury. She is often in control of the S.H.I.E.L.D. helicarrier when Director Fury isn't at home. She holds the rank of Commander and often addressed as such.
- Maria Hill is the Deputy Director of S.H.I.E.L.D., and also bears the title of "Commander". She enjoys a well-deserved reputation as tough-minded and by the book. Her clear-headed pragmatism is a valued source of reason during the critical discourse surrounding the Avengers Initiative.
Victoria Hand is a high ranking agent of S.H.I.E.L.D. with a level 8 security clearance level. She is considered an excellent operative and demands excellence from her staff and agents who report to her.
- Victoria Hand is a high-ranking Agent of S.H.I.E.L.D. with level 8 clearance. Hand is well-known to lower ranking agents and has a reputation for brusqueness and expects promptness from agents under her.
It is difficult to determine what information these three operatives would have in relationship to real world information management agencies such as the Central Intelligence Agency (CIA), The Federal Bureau of Investigations (FBI), and the Department of Homeland Security (DHS).
S.H.I.E.L.D. would be considered having access to information from such agencies in addition to their own specialized information databases regarding metahuman and extraterrestrial threats. Since metahumans engage and cross over into activities that most intelligence agencies are involved in, S.H.I.E.L.D. would likely be involved.
- The Strategic Homeland Intervention, Enforcement and Logistics Division, better known by its acronym S.H.I.E.L.D., is a secret United States extra-governmental military counter-terrorism and intelligence agency. With its advanced weapons and extraordinary agents, S.H.I.E.L.D. is maybe the greatest military power on Earth. Run by Nick Fury in the modern age, S.H.I.E.L.D. has to deal with all kinds of superhumans, gods, and extraterrestrials.
Because these characters have quite extensive histories in the Marvel Universe, I have included links for anyone interested in historical references to the characters.