Market
From the City page, click on the Market icon found on the main page. You can also narrow your search, by clicking on the Shops button, and clicking on the market tab there. Here you can buy items that other people are selling. To sell your own item, you must first buy a Stall in the City Hall. From there, click on your Business button, now available on the City page.
On your display section, choose which item you have, in your Inventory and select it. Pick how much you want to charge for the item, and click offer. Once your item sells, check your Professions page to see if the item sold.