The Wolf of R-Wall Street says: “The main purpose of the stock market is to make fools of as many men as possible. So basically, it fits right in.”
Cargo can gain credits to buy useful station supplies in two ways: exporting valuable goods to CorpComm, and playing the stock market for fun and (maybe) profit. Only one of these can be done from roundstart. Even if you've got a robust mining department and the ship is cooperating to provide the department with a steady flow of exports, Cargo Technicians and Quartermasters will want to master the art of the deal. And anyone can play, if they have the money and the patience…
There are Stock Exchange Consoles in every room in Cargo, as well as the Stock Exchange Room. These are all-access, so anyone can invest their money, even Civilians and Tourists; however, the Quartermaster has a special Cargo Budget card for playing with the department's finances.
The console can be set to Full or Compact mode. For basic trading, Compact mode will do just fine, but if you want to perform more advanced trades, you will need the full view. Both modes provide the following:
The basic principle of the stock market: purchase stocks at lower costs and sell them at higher costs. This is a good general rule of thumb, but there is some nuance to it:
Generally speaking, to maximize one's profits, invest in the stocks that are rising in value the fastest. These are usually mid-to-high-range in initial share price. Always check the history!
Of course, it would be wrong to attempt to manipulate the market for personal gain, not to mention incredibly difficult unless you have help. Here's how to pull it off, simplified. Note that this has significant dangers if not used against the right stock – or if you can't buy enough stock to make this happen.
First, you need someone (likely a department) with a lot of money, to buy up a large amount of a particular stock. The stock will naturally increase in value in most cases - that'll tell you when you're having an impact.
Second, another wealthy benefactor (likely another department) with a lot of money engages in the short sell. They get money equal to the number of shares they buy times the current value, but have to pay back the value of the stock at the level it is when the short date comes up.
Third, before that date comes, have the first benefactor sell all of their stock at once. This will flood the market and drive the price down, hopefully making both benefactors a lot of money in the end.
Of course, there's one more element to making money on the stock market, and that is knowledge. Watch the news and current events; if civil war erupts, body armor and weaponry will not only increase in cost at the Quartermaster's, but their stocks will likely increase as well. If somebody announces an active investigation into a company, their stock will likely decrease as nervous investors sell off their shares. If you can get inside knowledge of a particular company, you may even get advance warning when one of their stocks is about to increase or decrease by learning of news in advance. Syndicate-associated stocks, in particular, tend to drop in value when your ship destroys Syndicate holdings, particularly those specifically allied to a particular company. A particularly mercenary crew could declare war on the Syndicate just for the stock options.
(To be added: guides to other aspects of stocks, the full console mode, etc)