When you gain a Class Skill, choose one of the five Class Skills shown on your chosen Class card and tick the box to the left of it. Your Hero may now benefit from this Class Skill. A description of each Class Skill is shown on class skills.
You gain a new Class Skill at each level starting at level 2. Therefore, by the time you are level 5 you will have gained four of the five Class Skills shown on your chosen Class card.