Characters have a set of abilities they can use on their journey.
You can learn more by checking Stat.
Every skill have a "special application", defined by the activities that require an extensive dedicated learning process to be properly applied. For example, proper administering of medical actions is a complicated process that can not be done by a bystander. Is the character tries to use this special application without training - they will use not the bonus amount of d3 rolls, but the special negative roll. The formula look like this: "3d6 + stat mod - 1d3". This should negate some stat mod bonus as a consequence of doing-without-knowing.
At the character creation their background allows them to have some special applications known. They can learn to use some more in their journey at the discretion of Game Master.
Incomplete list of special applications is as follows: