You can attempt to dodge attacks against you by rolling against your dexterity, adding your armour points to the result. To suceed, the result must be under or equal to your dexterity attribute. If the attack is from an unseen target, you may not roll to dodge the attack.
Certain enemies will also attempt to dodge your attacks. For this, you must roll against dexterity, subtract the opponent's armour points, and subtract the extra damage your weapon deals(representing weapon length, and specialist enchantments which pull the sword to your foes).
You may also attempt to parry incoming attacks. Roll against strength, subtract weapon damage, and add half of the opponent's bonus damage. So, as an example, let us say that there is a warrior with a doubly enchanted large 2h sword that is fighting a mammoth. This is what would be done:{1d20-3+1/2(1d12)}. If the attack is from an unseen target, you may not roll to parry the attack.
Incoming non-magic ranged attacks can be blocked by characters carrying a shield. Roll against dexterity, and subtract the armour value of the shield multiplied by 4.
Magic attacks are trickier to defend against. You must first roll against wisdom, to perceive the incoming threat. Then, roll against intellect to prepare your mind and body against the incoming attack. Finally, you must roll against constitution to absorb the spell unharmed. If the spell is from an unseen target, you may not roll to resist the spell. You can only resist 1d4x1/4CON spells per day.
There is a much easier way to defend against magic attacks however. One may come across and equip a mirror shield. If that is the case, treat the roll the same as a non-magic ranged attack with an added wisdom roll beforehand.
Performing a defense action will prevent a movement action on your next turn.