Active Modules are trigger Abilities/Skills that can be bought or sold and fitted into slots that are numbered One(1) through Four(4). Once modules are placed they can be used by pressing a number on the keyboard corresponding to the numbered location of the module.
The amount of Active Modules per ship depends on the Tech level of said ship. Current ships have no less than two and no more than four Active Module slots. Some modules may be used by all classes of ship while others are specific to certain roles.
Note that Module effects typically do not stack. So if two Command ships are within range of providing an Aegis buff to your ship, only the stronger Aegis effect will be applied.
Hierarchy of Module Efficiency
The first level of item, bought from the warehouse with credits.
Created by upgrading a Mk I item, either by paying credits or applying an upgrade kit found as loot.
Created by upgrading a Mk II item either with Galactic Standards or Loyalty Vouchers from the correct faction for that item.
The most powerful kind of item. Created by upgrading a Mk III item with an experimental upgrade kit, or by paying Artifacts.