Strength
Strength affects heavy weapons usage (including bows),damage bonus, stamina, maximum carry weight, maximum armor weight and visual body strength.
Dexterity
Dexterity affects movement speed, stamina, jump height and weak spot chance.
Constitution
Constitution affects your health, stamina, maximum carry weight and maximum armor weight.
Psyche
Psyche affects your mana and resistance to magic.
Intelligence
Intelligence affects your mana, effectiveness with magic and book reading speed.
Size
A higher size attribute increases your height,weight, health and damage bonus. You can increase it by eating certain foods if you have available attribute points.