Capital Ships

Capital ships are the the class of biggest and heaviest mass produced ships in the Galaxy. They are also almost absurd in terms of their upkeep, which makes them spend most of their time on planet orbits, in times of peace departing from them only for occasional inspection or military excersises.
In times of war, however, they are a main fighting force of any real navy. Only capital ships are durable enough to actually receive hits from another capital ships and continue fighting. All 'real' star battles can be described as entire squadrons of battleships or dreadnoughts firing at each other - sometimes for quite long - with missiles and cannons, with each of their salvoes strong enough to obliterate whole planets.
As such actually constructing them is a very complicated (not to mention costly) process, that requires immense knowledge about construction technologies. With many secondary powers of the Galaxy actually prefering to simply buy them from more advanced countries rather than invest in expansive (not to mention costly) scientific and engineering projects required to introduce their own class of capital ships to the Galaxy.

Variants

Pocket Battleship - Slightly slimmed down version of typical battleships. They are nearly as powerful in terms of armour and weaponry as his 'older brother', instead having powerful engines and great gravity sensors, also with hangar deck dedicated to hosting at least a squadron of corvettes. In short - they are dedicated for convoy raiding, capable to operate independently and decimate every convoy's escort (with even few heavy cruisers failling to force it to retreat) and then sending corvettes to catch fleeing cargo vessels. Thus forcing their enemies to delegate battle cruisers or even capital ships for convoy protection. 2 000 000 tonnes and up to 4000 mariners.
Battleship - A classic variant of capital ships that serves as a basis of most starfleets. Relatively fast (or at least faster than ponderous dreadnoughts) with mighty weaponry and armour. Their tactic is quite simple, they just intercept their enemies and fire for as long as they have ammunition or until one of the side considers itself defeated and flees. 3 000 000 tonnes, with up to 5000 mariners.
Fast Battleship - Fast battleships are a variant of capital ships dedicated to be maneuverable and faster than typical battleships, while still being capable of prolonged firefight with them. They tend to form a small minority of capital ships that are supposed to engage in maneuvres on the battlefield and raids attacks various fortification systems. They can obliterate everything they can't run from. Battleships will still defeat them, but due to them being mostly slimmed down in terms of armoury (with actually reinforced weaponry) they tend to come out of the battle in rather bad shape. They tend to have around 2,5 to 3 000 000 tonnes, and up to 5000 mariners and marines.
Dreadnought - Biggest class of capital ships, used by majority of fleets but only by few as the basis of their naval powers. Most tend to use it simply as flagships, leaving the rest to much faster battleships. On the other hand, there are also fleets that prefer dreadnoughts. They have 4 to 5 million tonnes of tonnage, and up to 10 000 mariners and marines. Sometimes they are also called superbattleships.
Voidcraft Carrier - Voidcraft Carriers are a standard class of ships dedicated to delivering voidcrafts and corvettes to the battlefield, encountered among majority of space fleets. Their sizes tend to be similar to battleships, which allows them to carry an impressive numbers of smaller units.
Voidcraft Supercarriers - Supercarriers are a ship class dedicated to delivering voidcrafts and corvettes to the battlefield, that is, however, much less widespread than Voidcraft Carriers, met typically in fleets that use voidcrafts as a very important part of their military doctrine. Their size tends to be similar to dreadnoughts.
Monitors - Monitors are super heavily armoured and armed ships, that are also slow and incapable of maneuvring, created with piercing through fortified bottlenecks (for example hyperlane's exits) or attacking heavily fortified planetary orbits and so on. Constructed with battleships in mind.
Heavy Monitors - Heavy Monitors are super heavily armoured and armed ships, that are also slow and incapable of maneuvring, created with piercing through fortified bottlenecks (for example hyperlane's exits) or attacking heavily fortified planetary orbits and so on. Constructed with dreadnoughts in mind.

Configurations

Ships of the Line - Ships of the line (sometimes called artillery capital ships) are the baseline capital ships armed with variety of artillery weaponry, with missile weapons being secondary in weight. With decent AV defense and powerful shields. They serve as a basis of all serious fleets of known Galaxy. Resilient, powerful and reliable, rathen than unpredictable missile ships.
Missile Capital Ships - Missile Capital Ships are a type of missile ships, just greater in scale. That tend to be armed with few heavy cannons for self defense against cruisers, and as much SK missile silos as it is possible.They are unpredictable - depending on their commander skill and luck they can either cause truly massive, crippling damages... or none at all. They are oftenly met only among fast battleships, that can fire salvoes one after another while keeping safe distance from hostile battleships.