You can customize each of the categories above (except devices) to create unique ship classes.  Your empire's ship classes will not be known to other empires unless you give the design to them, or they salvage the design from one of your destroyed ships.   When you first encounter a foreign ship of an unknown class, you will be able to tell only that ship's class name, tonnage, and operational rating.  All other characteristics will remain to be discovered.

At the start of the game your empire knows the basic designs for each ship category, all devices, and the starbase class of orbitals:

There are three ways that you can add new classes to your list of known ships:

1. You can design new ship classes.  Your empire must pay a one-time design fee equal to half of the cost of an individual
   

   ship of that class (rounded up).  Missiles are exempt from this one-time design fee.  See the Create New Ship Design phase.

2. Class designs can be given to other empires without cost to either party.  See the Give Ship Designs phase.
3. The wreck of a ship destroyed in combat can be salvaged (under specific conditions), examined, and reverse-engineered, also without cost.  See the Salvage Designs phase.

You can build a ship on the same turn during which you research, salvage, or receive that ship's class design.  New ships can only be constructed at worlds which you or your allies own, and the necessary RUs must be present on the worlds where you plan to build.  One of the dangers of interstellar combat is that an enemy can take possession of your worlds that are slated to build new ships; in this case, the pending build orders become void.