There are three main types of Resources in the game – Food, Gold and Iron. You need them to construct Buildings, discover Lost Arts and produce and maintain Units. The amount of Gold and Iron you can produce per hour depends on the number of Resource Buildings you have built and their respective Levels.
Moreover, there are special Resources called Maranian Amulets that enable the training of powerful Units. You can obtain these by exchanging Gold and Iron for them, or by capturing and holding an Amulet Shrine.