For this you simply press and hold X until something tries to hit you with an attack that allows you to parry. If you can parry the attack there will be an icon with an X in it before the creature attacks and as soon as it hits you while you are holding X it will be followed with an icon to press B in order to counter attack. As long as another party member is near you when you do this it should trigger a link attack and you will get the achievement.