To perform a combo, attack an enemy until your XP bar is blinking red (if you are using the class UI, your XP bar will go above 100%). Then, press A, S, or D in a sequence. If done correctly, your attacks will chain and you will perform a combo. When your character says a phrase, you have successfully performed a combo. To find out all of Seal Online’s combos, visit: http://sealonline.wikia.com/wiki/Combos