Attacking is a standard action that consumes the Philosoper's turn. This begins with you, choosing a Skill. You then roll a d6 die for each rank you have in that Skill, and add that to your character's Credibility score. Divide that number by five (round down), and you have the amount of Hit Levels you have dealt in damage to your chosen enemy!
If you use an Ability that modifies your Attack, however, you must choose the Skill that corresponds to that Ability, or you cannot use it. You have been warned! This goes for Abilities that affect Defenses, too.