To learn most of the various techniques in Jadian, you must "learn" them with lessons. Lessons can be gained many ways. You get two Lessons when you begin your life in Jadian. You also gain 1 Lesson per Level Up, and gain lessons for various Class Level Ups. You'll almost always gain lessons after completing quests, and you can buy lessons from shops, if anyone sells them.
Also, there are a few other ways to learn techniques. One is to buy them in shops (they are usually quite expensive, however). Another way is to Class Techniques, or techniques you get for reaching a certain Class Level. Finally, certain races have access to certain techniques. However you choose to do it, learning techniques should be simple.