Stations are all over the map. They are a place where you can trade items with the station, repair, or just sit in it's safe zone and chill out. A station's safe zone makes you safe from all attack, fish and player alike. Stations have a feature which allows you to "Trade" items between them. You can buy an item at one station, and sell it at another, usually for a higher price. The prices can fluctuate, however, depending on how many people have bought that same item before you, so watch what you buy!
On the map, there is a special area called the Battle Zone. There are 3 stations in the battle zone, one for each faction. It's function is what it's name implies- a place for open PVP. Protective seals don't apply in the battle zone. Certain stations have a "portal" to the battle zone, when, when clicked, will transport you instantly to your faction's station in the BZ.
Station-to-station trade is a quick and easy way to earn large amounts of Cel in a short amount of time. Each station on the map has it's own individual list of what can be bought and sold there. Some pieces of flotsam you pick up also can only be sold at specific stations, such as if you pick up some Plutonium or Lead, you can only sell it at stations that are buying Plutonium or Lead. The trade prices also fluctuate based on supply and demand, so if you do the same trade route over and over again, or do an overrun trade route, the prices will start to suck and eventually you will start losing money. The stations also have a finite supply of items that can be bought, with a max of 10,000 "spaces" of all items that can be bought. Once this reaches 0, that item is considered "out of stock" and can't be bought anymore. The amount is automatically reset at the server restart each night. Some trade routes, while giving lots of cel (like a platinum run) are dangerous because for a jaf or scion, Platinum bought at Lima can only be sold at Chelos or Nijam, and a long the way to both stations there are a LOT of high level fish. So, long story short, try to stick to trades close to your level, and don't do trades until you have a level 15 cargo ship, which has a max cargo of 200. Until then, you're actually better off collecting flotsam.
External Link Edit
Deepolis Trade Routes A fully interactive map with all the known trade routes. Just click a station to see what goes where.