You can use your market to trade with other people who live in your province.
(a region marked with red lines on the map).

You click on a tab to choose the resource you want to trade. Then you choose whether you want to buy or sell the resource, the amount of the resource you want to buy and sell, and the price in gold you will pay or charge for each unit of the resource.

Once you have made your offer, the market either matches it with a current offer/request or posts it for such time as an offer/request occurs. Good offered up for sale become unavailable for your use, until such time as you cancel the offer.

A fee is charged when you make the offer and is not refunded if you cancel it. It has been reported that the market does NOT protect goods that have been offered from being raided.