Materials are needed to craft items. For this you will need to gather raw materials and refine them. The more rare a raw material is, the longer it will take to refine it.
Each gatherer profession can gather 3 different raw materials and each refiner profession 3 different refined materials, each having its own rarity (common, uncommon and rare).
In the coming expansions / updates we will add more materials, even more rarities and they will also be needed for building your very own buildings.
Down below you can check all the raw / refined materials, which professions are needed to gather / refine them and some example recipes for the refining process.