Skills

That which all can do, and in their so doing make the world.
They are tested by rolling 1d6, succeeding if the result is equal or less.
To gain them costs 10xp per rank. (10xp for level 1, then 10 more xp for level 2, etc)
You must find a teacher or another reasonable way by which you may learn or improve.
They range from 1-5.

While this skill list contains many common things that characters may attempt, it is not exhaustive, and you are encouraged to create your own.
In general, a skill simply denotes a specific act that itself requires training in order to improve at.
For example, if your game takes place in a society that lives underground or along the sides of sheer cliffs, there may be many specific skills that people there understand and train themselves in.
Simply list them, describe when a check involving them would come into play, and improve them as any other.