ROM: Golden Age features various skills for each class.
Basic skills can be learned by purchasing 'Common' and 'Class-specific' skill books from 'Skill Book Shop' NPCs located in towns or safe zones,
then double-clicking the skill book in your inventory.

Skill books can also be obtained through monster hunting or purchased from the Auction.
If you have a skill book for a skill you've already learned, you can use it to enhance that skill.