You have three options:

1. Dodge

2. Endure      

3. Get Hit (fall over and start dying)

Dodge - Your Dodge skill plus any item modifier

If your dodge rating is higher than the attack rating then the attack misses and you take no damage.

Endure - Your Endurance skill

If your endurance rating is higher than the attack rating then the attack hits but you have lessened the damage. You have been lightly wounded.

Get Hit - If you have no Dodge or Endurance rating, or they are not high enough then you take the full damage of the attack. You have been mortally wounded.

You can only defend against each attack once.

You can only defend against a number of attacks equal to your skill rating. Skill ratings refresh after half and hour.

If you're hit then you must react or recoil. It would probably hurt!