Skills are a core part of gameplay in Pillars of Eternity and Pillars of Eternity II: Deadfire. Skills come to play in a variety of different contexts and partially determine how the player character or their followers can interact with the world around them. A character's skill level is represented as a number, which in turn represents their proficiency in performing certain tasks, as well as their knowledge of fields associated with that skill.
Many skills have a direct impact on game mechanics, and allow your character to perform specialized actions like stealth, detecting traps, picking locks, or reading scrolls. A more skilled individual will perform these tasks with ease, and will have a higher rate of success.
Some skills grant auxiliary combat bonuses, either directly affecting attributes - or other combat mechanics.
Outside of combat, skills play a large part in dialogue and scripted interactions, where they can be "checked" to overcome an obstacle, and determine whether a character succeeds or fails to perform an action. Having more points in a skill can also unlock additional dialogue options with NPCs, which can be invaluable when pursuing a specific outcome for a quest or conversation.
In Pillars of Eternity
In Pillars of Eternity the five skills are:
Every class gains an initial proficiency bonus in two skills, but not limited to them. Non-combat skills are gained separately from combat skills (Abilities, Talents), and they do not use the same resources.
In Pillars of Eternity II: Deadfire
Pillars of Eternity II: Deadfire sees a large expansion to the skill system. Many new skills have been added, and are split into two categories – "Active" and "Passive" skills. When the player levels up, skill points are split between the two groups.
Passive skills cover checks in dialogues and scripted interactions, and otherwise have no bearing on other parts of gameplay. Active skills are also used in these checks, but more importantly provide boosts to other game mechanics (hence "active"). For example, having a higher Explosives skill improves a characters ability to use bombs.
Another addition is the use of "assisted" skill checks, which allows the player character to benefit from other companions' skills. Certain checks are limited to the only checked characters' skill level, while others use an "assisted" value, which applies a bonus which takes into account every other party member's proficiency in that skill. 
- Pillars of Eternity:
- Class - 3 skill points in total, distributed irregularly.
- Background - 2 skill points in total, distributed irregularly.
- Pillars of Eternity II: Deadfire:
- Class - 2 skill points each for 5 different skills. A multiclass character limits this to 1 point, with overlap being added (the note in the character creator regarding "averaging" skill bonuses is misleading).
- Background - 1 skill point each for 3 different skills (with some exceptions receiving two points in one skill, or 3 points in a 2-1 split).
At each level, the character will receive skill points that you can distribute as you see fit.
- Pillars of Eternity: 6 points to distribute. Advancing a skill costs 1 + the skills current rank, not including bonuses (via items, class, background). At skill level 3, it costs 4 points to advance to the next rank.
- Pillars of Eternity II: Deadfire: 1 point for Active skills, 1 point for Passive skills.
Items and other bonuses can also increase skills, be it while equipped, permanently, or as a temporary bonus. Items that grant skill buffs are shown for each skill, on the associated page.