The Imperial Navy is the Starfleet's main organization in charge with the defense of the interests of the imperium and it's people. Having always in mind that the most important thing in the Empire are the people not the goverments. A goverment is just an instrument of the people to coordinate their efforts. The weapons of the Empire must be used to protect the people , never to harass others . The Navy is divided into several military components.When there's a situation that involve all the components we are talking about Navy's stuff, but in normal things , only the main components are involved and we are talking about Imperial Armed Forces.While there's some components that serves mainly as a reserve , there's some components that follow a specific purpose and works close with other military services . Although the structure is complex,  allow us to organize our forces in an efficient way.

Standard Organization:

The Imperial Navy is organized into fleets, which are composed of one Victory/Imperial-class Star Destroyer accompanied by support and lesser combat ships. Each fleet can operate independently. In practice , Star Destroyers can be combined in Task Forces of three, Sector Squadrons of six, or Regional and Territorial Fleets of 24 - but it is unusual for more than one to occupy the same star system, except for ceremonial purposes. Such concentrations of force are rarely necessary- there are few things which can seriously challenge even one Star Destroyer.

Real Organization:

At this time , there are several things who can challenge and defeat our Star Destroyers and there's the fact that the SD is no longer a distinctive vessel of the Empire, the Republic Navy and even some civilian elements are the owners of a certain number of captured Star Destroyers. Also, the Republic itself not only captured some Star Destroyers ,but started the construction of both Victory-class and Imperial-class Star Destroyers and researched new class of Star Destroyers like the Defender class. Given also the fact that the Republic managed to destroy our Star Destroyers using a minimal amount of pilots, The Empire decided to use more than one Star Destroyer in a fleet. The introduction of the Hidden Fleets changed the usual point of view that the Empire had about fleet organization. Imperial Standard Fleets may still be like the by-the-book ones but non standard fleets or task forces may have hundreds of vessels assigned , from all classes , starting by the Lancer Frigates , Corvettes and Carrack Cruisers up to Vengeance Battlecruisers (or Vengeance class Star Destroyers) and/or Super class Star Destroyers.There are also Standard Fleets that are assigned to standard duties but have several Star Destroyers and we recently started to use the vessels we have captured all this years from Republic and neutral hands like calamari cruisers and dauntless cruisers but we have just a few operational cal and two dauntless. The rest are still under repairs and /or refiiting to reach imperial standards) or they are not available due to internal law stuff like the authorization forms. 

The Navy's main components are the Armada , the Army and the Air-Space Force.

The Imperial Armada duties include navigation, ship managing, ship crew duties, ship command, ship to ship combat, fleet command, fleet combat, fleet bombardment. Imperial Armada officers are also trained to perform in other military services : they recive general troop and mech training , starfighter /transport pilot training . The Armada itself can work as an independent armed force,freeing the  other components duty roasters allowing them to have more elements to act and reinforce their positions.

The Imperial Army duties are to practice and apply martial Arts, self defense, survival skills, solo operations, guerrilla, commando, ground combat, infantry, artillery, mech , patrol, ground command. they have  little training in ship duties just in case they are requested for such a task as well as transport pilots.

The Imperial Air Space Force duties are to learn, practice and apply flying skills, combat flying skills to help protecting the sky of our planets and our deep space territories. They are trained to fly everything from fighters up to the helm of light starships . They had also a little training in army duties and they work very close with the Armada component.

The Imperial Guard is in charge of the garrison of the Imperial territory and customs stations.They recive standard army training.They deal with any internal threat to the Empire.

The Imperial Royal Guard is in charge of protecting the political leaders, such as the council of lords or the Imperial Senate and our Navy's highest rank officers as well as some other key personnel.

Imperial Police is the one that keeps the law and order in the civilian zones.

The IIS (Imperial Intelligence Service) is permanently finding information about any threat to the Empire and it's citizens. They provide the info to to the Navy's high command and they consideering the data , take the necessary desicions to protect the Empire and it's citizens.

The Stormtrooper Legion is yet another way to provide our main forces with a continuous flux of infantry reserves, when needed, as reinforcements. This is specially  useful in war . The Stormtrooper Legion is continuously accepting new volunteers from any race . Balance comes with many people different, each race covers the other race's disadvantadge and the imperial forces will recive more support when the people realizes that it is a multi race force looking for equality harmony and justice instead of ruling thru fear of force.  

The Civilian Defense is an organization always ready to respond when a natural dissaster occurs. They also help with the traffic organization and some other things to help and protect the civilian elements.

The Security Cartel have the mission of protecting the strategic imperial facilities.

Finally, the Core Division is the one in charge of organize and coordinate the efforts of all Navy's components , they also are the link between the Navy components and the Unified High Command (UHC) (or Navy's High Command) . They are in charge of all the protocol and administration of the Navy's structure , facilities and resources with the approval of the UHC. 

 The UHC (Unified High Command) is the one that led the whole Navy. The UHC is conformed with the highest rank offcers from all components.