If your character is armed with a weapon or shield
that could parry an attack, he or she may roll against
the relevant weapon skill to parry the blow. You do
not need to announce this beforehand, and it is done
in reaction to a successful attack roll from another
player or non-player character.
This tells me nothing,
what do i do if a character with 75% shield skill and a half shield, tries to parry an attack from an NPC with a hand axe and 40% axe skill? The attack was a success.