1 Advance to the castle age
To build a trade cart you need to build a market and to build a market you need to advance to the castle age.
2 Build a market
The market is the building where you can create new trade carts so that you use them for trading.
3 Your ally must have a market
Trade cards can't be used unless you have an ally who has a market. If you don't have an ally or if your ally doesn't have a market, then trade carts will be useless.
4 Create trade cards
After making sure your ally has a market, create one or more trade trade carts depending on your needs.
5 Direct the aarts to the ally's market
Select the trade carts then while they are selected click on the market of your Ally. This will let your trade carts start moving between your market and your ally's market for trading.
6 Direct new units to the market
You can also set the flag of the newly generated units directly to the market of your ally. In such a case, generated carts will automatically start trading.
7 Use trading upgrades
Make upgrades using the market to improve the trading process and bring more Gold.
8 More carts = more Gold
Trading brings gold. The more carts you have, the more gold you will get. Also the bigger the distance between the two markets, the bigger the amount of gold will be.