Grisha use what's already there, inside them, and train to use the Small Science to hone their abilities. There are Grisha would are called Alkemi. They specialize in poisons, healing liquids, and powder, typically blasting powders. Everything else, the knowledge of combat, the strategy of a fight or war, the history of our people, the languages of other people, etiquette classes, and handwriting and math instruction are all in addition to our Grisha abilities, which are innate and not a skill.