In Evony, the market is a very simple, yet important building. You may construct one by clicking on an open building spot in your Town and clicking on the market. You will need a small amount of resources to build it.
A market is your source for selling surplus resources and buying resources you are in need of (Food, Lumber, Stone, Iron). The currency is gold. You receive gold for selling and spend gold for buying. Often, players will take advantage of high and low prices, and make a profit.