Not to be confused with avatar abilities.

Skills are what affect you and your enemies Chance of Damage in combat. You have a base skill level that raises up 50 points per level up to 400 total at Level 80 They may further be increased by Avatar Abilities, hence the confusion, and further increased by equipment.

For a full list of all equipment and the skill bonuses they contribute, please see the Equippables Database

To view in game, visit the Character Tab>Information page. You can hover over your individual skills to see a breakdown, like so:

There are Four skills total, 3 of which are weaponry related raising your Chance of Damage
Gun, Melee, Projectile Skill
And lowering your enemy's Chance of Damage, is your Defensive Skill

Unlike stat points, skills are gained through practice. Defensive skill is increased when you take damage, while the other three are increased by attacking for no effect.
Missing, which is determined by the Accuracy stat, does not appear to raise skills.

Mixed Weapon Bonus

This bonus was implemented to remove the disadvantage of wielding two weapons of unlike type (Gun, Melee, or Projectile). When carrying weapons of two different types, the player receives double the skill bonus normally granted by each weapon (see below for example).

When a player carries two of the same kind of weapon, they receive the skill bonus from each weapon. However, this skill bonus applies to both weapons.

Example:

Arm Blade gives +6 melee skill.

Rapier give +4 melee skill.

Therefore, each weapon will hit with +10 melee skill.

Without a mixed weapons bonus, players who carry two different weapon types are at a disadvantage, as the skill bonuses provided by each weapon generally only apply to that weapon type.

Example:

Revolver gives +6 gun skill

Rapier gives +4 melee skill

The Revolver will hit with +12 gun skill, and the Rapier will hit with +8 melee skill (both twice the normal skill value contributed by each weapon).

The same applies for weapons that give skill bonuses for more than one type of weapon.

Example:

Crossbow gives +6 gun skill and +6 melee skill

Rapier gives +4 melee skill

The Crossbow will hit with +12 gun skill, and the Rapier will hit with +20 melee skill (2*6 from Crossbow + 2*4 from Rapier).