Abilities are actions that can be learned by observing or discovered; once known, they can be executed any time, given the circumstances permit.
For example:
Building a fire might be discovered by spinning a wooden branch very fast between ones hands on another piece of wood. So this then can always be used. But depending on the used materials, it may go better or worse a next time (wet/dry wood, fatigue, etc). And over time, making a fire might be discovered by using two stones instead.
Skills can be seen as abilities that can be taught by someone else or discovered and can be improved by more teaching or exercising them.
For example:
Starting as a novice blacksmith, one needs to learn how to melt ore. This will not go 100% fine at first, meaning loss of resource, contaminated resources, low quality etc. By doing it more often, this will improve. Even combinations can be found (like coal + iron -> steel) by exercising this more.
So very short:
The result of executing an ability (in whatever way) will always be te same, whereas using a skill, the higher one is proficient with the skill, the better the outcome will be.
Skills can be grouped together to form a profession.
For example Blacksmit:
- Skill smelting
- Skill tempering
- Skill smithing
and so on and so forth
