You can pierce your suit, weapon, and shield in FlyFF to gain addition stats and effects.  All the piercing is done the same for all types of suits, weapons, and shields.  Weapons and shields can be pierced 10 times, while suits can be pierced 4 times.  (NOTE: Two-handed weapons can be pierced 20 times.) These are the steps and items you need to pierce your equipement.

Weapon Piercing

Suit Piercing

Piercing Cards