I've been moderately successful trading (not quite enough to buy a new freighter, but I'm getting close).
- You need to discover places that BUY (denoted with a "+" outside) and places that SELL (denoted with a "-" outside)
- 99% of the time I use the MENU(4) option (or SHIFT + T for the lazy)
- Your ship (unless it's a small ship, meaning flown by a pilot, not a captain) will need Cargolifter URVs. You can buy these from Ship Dealers by equipping drones. (If there is a ship being constructed by that shipyard, you can't buy the upgrade there)
- Find the good you want to buy and sell. Switch between buy and sell by clicking the "To Sales" and "To Offers" button.
- You can expand offers by clicking the "+" next to them on the left
- Ensure you have the right ship selected (it gets reset to the first ship in your squad)
- Buy the good from the station you want, it should default to the max amount you can afford, the max amount they offer for sale, or the max amount your ship can hold.
- Switch to the "Wares bought by station" mode ("To offers") and sell your goods. It should also default to the max amount that they are buying, or the max amount you have (there might be a bug here regarding overselling).
- If your captain says they have insufficient fuel, click on their face and choose the dialog option for them to buy fuel. If you don't, they will still go towards their destination, just without opening a jump tunnel.
- Once your ship gets to the destination, it will tell you they are loading or unloading the wares. This takes a while.
- Each Cargolifter URV can only move so much, so the more Cargolifters you have, the faster the loading and unloading will be. I have 10 cargolifters on my Construction Vessel and it takes about 5 minutes to move 20,000 food rations, however I haven't seen any actual drones launched, but it does seem to work.
- Buy the freaking trade computer when you can afford it. You still have to fly near stations (Solar I, Solar II, Solar III are different stations) but flying near them will add all their shops to the potential offers. It saves you a lot of time trying to get within 500m of the store front, or not seeing a store.
- Added Don't watch your trading ships (except via the map "," key) They're a little pee shy, I think.
I'd suggest not setting up more than 2 trades at once. It seems to be a bit more stable. One to buy, one to sell. If you need to setup multiple selling trades, wait until it's finished.
I've had to edit my save many times to clear up "stuck" drones, but I'm thinking I may have just been too impatient.