So there's a new thread asking for help with trade, and rather than write a little post there I'll write a short guide here.
Trade is perhaps the most important aspect of your nations economy- It can easily yield a lot of gold with minimal input on your part.
When you first begin, find out how many "trade" ports you have. If you don't start with one you should change one of your ports to a trade port. To do this click on the port, then on the building icon on the UI. There is a button on the left with a torch, click that to destroy the current building. Next turn you will be able to build one of three different kinds of ports. (Pick trade).
Also in the beginning you should send whatever navies you have to the different trade theaters. If you can only pick one or two go with Madagascar or the Ivory Coast (the African ones), as they seem to be the most lucrative. Place some ships on one of the gold "nodes" to reserve it for your trade ships.
If you have trade ships, send them to these nodes right away, otherwise build them as soon as you can and send them to your reserved spots. Trade ships have a gold coin on their portrait.
These nodes provide stuff like Ivory and Tea. You can see what your bringing in on the trade tab in your government window.
This shows a ship on a trade node. Notice that you can have more than one trade ship on a node, each one will earn you a little more money/bring in more goods.
You can also get resources from your territories, they show up on the map like in previous TW games. European regions seem a little sparse, so if you don't start with any regions in the New World or India, start looking to do so. When you locate some, build a plantation over it by clicking on it and then selecting the building to build. (Is this simple enough....?)
Once you have a plantation built you will make some money off it in that region, but to add those resources to your tradeable goods you need a trade port in that region, or an adjacent region that is connected by roads (I'm pretty sure).
Now that you have goods to trade, you need people to trade them to. You should have started off with some trade partners, and depending on how many trade ports you have you may be able to add a few more. Try to get deals with the larger nations, as they can buy more of your stuff.
The list of nations you are trading with is under the "trade" tab. This shows you what you are bringing in and from where. On the right side you can see how much you are making off of each nation. If one seems too low, you can always cancel that trade agreement and try to find someone else to trade with.
If the line showing the goods on the trade tab is red on either the incoming or outgoing displays, that means a port is being blockaded and the goods aren't moving.
Also, try to keep the better deals for as long as you can, because you start to earn more money on deals that have lasted for a while. I went from making 1000 to 7000 or so from the Ottomans this way.
This is the Trade menu.
The top portion shows how much each good is worth per unit. This number can change through out the game.
The Middle portion shows what you are bringing in from your empire.
Notice that America is bringing quite a lot because I have upgraded its plantations and ports.
The bottom portion shows what you are exporting.
Notice how much is being made from the Mughals and the Ottomans, both large nations.
Also:watch out for pirates and rival nations! One blocked trade route can cut off a large portion of your tradeable goods.
Ok, there's my simple guide. I hope it helps.