This is where the real business happens. Merchants from other countries come to the Trade Depot to set up stalls. They're looking to buy what you're selling, and they've got plenty of wares of their own as well. As you progress through the game, more merchants will come to do business, and their selections of items will increase.
At the Information Desk, you can check which items are recommended to ship, items that are on sale, and which countries' merchants are visiting on a given day. You can also accept requests from other countries.
You can buy items, animals, clothing or blueprints from the merchants who come to do business at the Trade Depot. You can also take on requests for specific quantities of items they really want, for which they offer good rates.
Eventually, you'll be able to open your own stall at the Trade Depot. Here, you'll be able to sell your crops or other things you've made on your farm. Townspeople and visitors will stop in and buy your goods if they like what they see.