Character Attributes affect a character's successful use of their skills. The following information was extracted and edited using the in-game book "Character Attributes". Higher skill levels increase stats during a level up, high sword skill ups STR.

Strength (STR): A scale to represent a person's might. Persons of higher strength hit harder and may carry more equipment without being fatigued. With 5 or more Strength, characters can manually push boulders.

Increased by; sword, mace, axe, polearm.

Dexterity (DEX): A scale to represent a person's quickness. Persons of higher dexterity may both move quicker and be surer in their strikes, while also being more capable of dodging incoming hits.

Increased by; ranged, locks.

Constitution (CON): A scale to represent a person's fortitude. Persons of higher constitution endure pains and hardships better than those with the lesser, and may also be quicker to recover from ailments. Poisoning from Giant Spiders is not affected, however, and will always last 10 seconds.

Increased by; shield, swimming.

Intelligence (INT): A scale to represent a person's wits. Persons of higher intelligence can deduce and execute our mystic and magical methods better than those with a lesser intelligence.

Increased by; magic, casting.

Perception (PER): A scale to represent a person's senses. Persons of higher perception may pierce the night's shadows better than those with lesser perception.

Increased by; stealth, appraise.

Charisma (CHR): A scale to represent a person's charm. Persons of higher charisma may have better luck in the coercion of others, particularly in trade and in the battlefield.

Increased by; leadership, trading.

Admin Notes
I'm actually taking a guess at how the player levels up stats, 
not entirely sure if I am correct. It's hard to tell when a troll
is trying to club you into a smushed patty! I notice your skills 
level up regardless of if your level increases, so I logically guessed
that your stats go up based on your skills. (based on the descriptions)