Well ability files are just that: abilities...
Each ability in the game has one ability file for it that includes information such as cooldown, AM cost, requirements (such as XP or technology), number of levels, whether it is passive, etc...however, abilities are quite complex, and usually require one or more buff files to make the ability work...
For example, take a simple AoE ability like Energy Aura...these types of abilities usually require 2 buff files to work...the ability file applies a "buff to self", naming the specific buff to be used...that buff in turn is a periodic action that applies another buff to all nearby ships every second or so...in this manner, a Halcyon carrier can improve the energy weapon cooldown of nearby ships, but only those in range of the Halcyon...
Some abilities only require one buff file (adaptive forcefield simply applies bonus stats to the Kol) while some don't require any (SB construction requires only an ability file)...there are a few abilities that require 3 or more buff files, where some buff files deal with entity modifiers (like bonus/penalty stats) and others deal with just graphical effects...
It is somewhat complex at first but but easy to learn and mod (you don't need any fancy programming skills, and most of the "native terms" are self explanatory, like "ApplyBuffToSelf")...
