Affinities
When a character of a particular type is good at learning a class or skill, that is referred to as an "affinity." Affinities tie different character options together and come in two varieties: Class Affinities and Skill Affinities.
Class Affinities
Generally, a character can only prepare one class action at a time for each level he or she possesses in that class. All non-human races, however, have one or more class affinities. A class affinity allows a character of that race to prepare one additional action of that class. The character must possess at least one level in the class to qualify.
Note that some races possess multiple class affinities. A character with levels in more than one such class, however, can prepare only one additional action, although that action may be from any one of those classes.
Skill Affinities
By default, skills are very costly. However, every race and class in the game has one or more skill affinities, which allow a character of that type to purchase the skill at a reduced cost. For example, warriors have an affinity for combat-related skills, so characters with levels in warrior pay less for those skills. Skill affinities come in three varieties: Weak (20% reduction), Moderate (40% reduction), and Strong (60% reduction).
It's important to note that skill affinities from your race and class stack, but skill affinities from multiple classes do not. When stacking occurs, two weak affinities result in a moderate affinity, and anything else results in a strong affinity. For example, an elf has a weak affinity for ranged combat and a ranger has a moderate affinity for it, so an elven ranger has a strong affinity for it. In the case of multiple classes with affinities for the same skill, however, only the strongest affinity applies. For example, warriors have a weak affinity for ranged combat, so a multiclass ranger/warrior has only a moderate affinity.
Note also that skill affinities are applied retroactively. For example, a wizard who later gains levels in warrior pays a reduced cost for Armed Combat, even if it was purchased before he or she ever gained levels in warrior.