Spaceward Ho! represents the entire economy of the galaxy with only two numbers: Money and Metal.
Money represents energy, food, manufactured items, educated people -- anything that can be replenished every year. If you can't run out of it, it counts as Money.
Metal represents things you find -- metals, oil, uranium, that sort of thing. Anything you can run out of is Metal. There is a limited amount of Metal in the Galaxy. Controlling the Metal can be very important.
You can spend money on lots of things: research, terraforming, mining, building ships, and so on. The only thing you use metal for is building ships. The more advanced ships take more money and metal to build.
That's it for the economy. Most of your decisions will involve how you spend your money. If you ever spend more money than you need for something, the extra will be conveniently saved. For example, if you spend $10,000 mining a planet that only has 100 metal left, the extra $9,000 will be put into savings, where you can use it later.
You never have to worry about moving Metal or Money. It will automatically just show up wherever you need it. You can mine it on the far right side of a huge galaxy and use it the very next turn on the far left side. This means you can build ships wherever you need them. Money behaves the same way -- you never have to move it to where you'll spend it. Forcing you to maintain supply lines would be more realistic, but it wouldn't be much fun.
You can choose different ways to spend your money depending on your particular philosophy and goals. The more money you spend on Tech research, the less you'll have left to develop planets. The more money you spend terraforming planets, the less you'll have for research, at least in the short term. Having more profitable planets gives you more money in the long run. Of course, it also means more places to defend. Decisions, decisions.
Remember that every time a starship is destroyed, most of the Metal used to build it is gone forever. This means that as ships are built (and destroyed), the material you build them out of disappears. Permanently. Near the end of the game, Metal can get scarce, and therefore extremely valuable.
When you spend money on most things in Spaceward Ho!, the more money you spend, the less value you get for your dollar. This means that it's better to spend $10 for two days than $20 for one day, unless you're in a hurry.
This makes it a good idea to keep your Tech spending steady. For example, if you spend only on Weapon Tech, then only on Shield Tech, then Range, and so on, your overall Tech levels will go up slower than if you spend a little bit on all of them at once.
This also applies to mining and terraforming. It's less efficient to try to do these things all at once than to do them gradually over a period of many years.
Diminishing returns does not apply to shipbuilding. Each ship costs the same whether you build ten of them in one turn or only one.
In Spaceward Ho! you can go into debt. This means that you can spend more money on shipbuilding than you've saved. You can borrow up to five times the total income from all your planets.
Unfortunately, you have to pay interest on your borrowed money. 15% of your debt will be automatically deducted from your income each turn. A high debt leaves you with less money to spend on terraforming, mining, and technological research. To pay off your debt, just put money into Ship Savings.
Experiment with debt. You'll notice that in the short term, it can dramatically improve your productivity, but over the long term it's likely to be disastrous.
The U.S. national debt is over $6 trillion. The government income is approximately $2 trillion. Gee, we wonder why there's so little money for growth. Hmmmm.
If you ever get into a situation where your total income won't even pay the interest on your debt, bad things happen. So far, we've never managed to recover from this situation. We highly recommend not getting into it.