Learn Skills & Spells
If a hero has learnt a new Skill or Spell, the unit does the following:
Learning a Skill
First, consult which skills can be learnt by the hero. In each warband's section, there is a table denoting which Skill Types they can learn. If the hero is a Promoted henchman, these learnable Skill Types will be listed under the Promotion Table instead.
Once you know which Skill Types the hero can learn, choose one Skill from among those Skill Types and add it as a Skill for that hero. Skills cannot be learnt by the same hero more than once.
A hero may also be able to learn 'Special' Skills. These are Skills exclusive to that specific warband. Consult the warband's section for a list of Special Skills (if they have any).
Learning a Spell
If the hero is a Caster, they can choose to learn a new Spell instead. This works similarly to Skills, except the Caster can choose a new spell from their relevant spell list instead. Spells also count toward the Skill limit, including the initial Spell the Caster learns when they are hired. This means that they can learn a maximum of three of the four spells available to them.