组成 (zǔ chéng) means 'to form, to make up, to constitute' — it focuses on the parts that together create a whole (e.g., a group, water, a text). Unlike 构成 (gòu chéng), which is more abstract and often used for legal or structural concepts (e.g., 'constitute a crime'), 组成 is concrete and everyday. 合成 (hé chéng) is narrower, referring to chemical synthesis or deliberate combination.