Designing your ships can give you a very significant advantage in the war on other empires.
There are two functionally different types of ships: Flagships and Support Ships. Flagships can be directly commanded whereas support ships must be assigned to flagships or planets, they can not be commanded individually. Every ship design is made up of subsystems which are placed on a hex grid.
Support ships do not carry their own supplies, supplies must be carried by flagships. When a fleet runs out of supplies it will not be able to capture any more planets and will experience significantly reduced combat effectiveness.
Ship designs consist of many subsystems of different types, each subsystem is a coherent whole consisting of one of multiple hexes. Most subsystems that span multiple hexes will have one hex designated as the "Core" or "Turret" hex. If a subsystem's core is destroyed, the subsystem as a whole goes down.
Railguns Provide a lot of dps, but they have a firing arc (meaning they cant fire in every direction) and a lot of their shots miss, especially when there is only one target. The shots fired spread out over a small radius, meaning that they don't hit on every shot. This makes railguns more effective against large targets like fleets of ships.
Lasers hit instantly and cannot miss, but they spread their damage out over time, making them vulnerable to being negated by armor.
Missiles do a lot of damage in a single hit, but cost a large amount of supplies to fire.
Rockets do a very large amount of damage in volleys, but have a very short range.
Plate Armor is the default armor type. It works decently against all weapon types.
Ablative Armor has less health than Plate, but has higher damage resistances. Ablative armor has additional increased resistance against beam weapons.
Reactive Armor is very good at reducing large hits, but fails against smaller hits.
Neutronium Armor has the most health of all armor types, but is extremely heavy and costly to build.
Liquid Armor has no damage resistance, but health can flow from high health hexes to adjacent low health hexes, providing a regenerating barrier until the entire pool of liquid armor is depleted.
All flagships and Stations have a maintenance cost depending on their size. Additional maintenance costs are added based on the components in the design. Support ships ordinarily have no maintenance cost, unless "supply crates" are added to the design.
For detailed costs see Table of Maintenance Costs