Money, goods, gold, and property, are all forms of wealth. It is the absolute backbone of an empire's economy.
Methods for Creating Wealth
You’re thinking: money sounds good! How do I get it? There are several ways, and what method is most effective depends on your playstyle. All methods are useful, however, and it is important to try lots of different ways to maximize your return. As just one example, on a large map it can be very handy to build additional survey ships (either armed or built with an escort) to scavenge anomalies for extra cash, among other things. How much emphasis and effort should be put into each method is a question of experience.
For most of the game, the wealth generated by colonies will be a large part of your income. Financial buildings (starting with the market or similar building) are used to raise the gross income of a colony. Researching Xeno Commerce early on is recommended; otherwise lack of funds may prove to be a serious problem for an empire. Specialization is important here where possible so that as little of colony production needs to be dedicated to money as possible. Planning ahead can be useful; for example, the financial capital provides a huge increase in income and has high adjacency bonuses. Keep a close eye on your colony setup. It might be possible to run only a very few "wealth" planets and maintain a balanced economy, while other colonies concentrate on research, manufacturing, or perhaps influence.
Tourism provides a safe, steady income that grows as your empire grows.
Generally, you will start with a ship that can study anomalies. Research will allow you to build a ship that can survey more widely. Placing a survey module on a ship will provide the survey capability. Note that your original survey ship is armed and at full health can deal easily with pirates that may be guarding anomalies. Survey ships built later will need armaments or will have to be escorted by combat vessels. Anomalies frequently supply cash rewards that can vary in their payouts, but uncovering a number of anomalies should produce a valuable addition to your income stream. This is valuable, particularly early in the game when the temptation to spend BC to hurry things along can be compelling.
Relics can be utilized by deploying a constructor within range of the relic, and choosing a precursor module. The first such module is the Xeno Archeology Lab, which gives a 10% empire-wide boost depending on the type of relic; higher level modules can be added after researching the appropriate technologies. Being able to grab a wealth relic is dependent on the situation, but like all other relics it makes sense to make a strong effort to secure one. In fact a war over relic(s) is not out of the question. Even at the first level, a 10% increase for your entire empire is a big advantage.
In order to trade, you need to first establish a trade route. To do so, you will need to send a freighter (built in the Shipyard) to another faction's colony. Most factions start with the capability for one route and can increase this by researching the appropriate technologies. The longer a trade route exists, the more lucrative it will become. There is also a pragmatic ideology trait that allows luxury trade routes that further enhance the income.
The existence of a trade route improves the diplomatic relations between the connected factions. This may, in some situations, be more important than the income, when for example one is fighting a war on one flank and is hoping to keep other factions at least neutral for the duration.
Sale of Items to Other Factions
You can consider trading Technology, Ships, Strategic Resources, Trade Resources, Colonies, and Treaties to other factions for BC. For example, at times you might obtain a colony that becomes untenable due to distance and enemy influence. Selling the colony to another faction then might be a smart move. A typical early game treaty sale to another faction is Open Borders, which allows ships from either side to move into each other's zone of influence without a diplomatic penalty.
Some trade resources affect wealth. For example, Ultra Spice increases gross income while Techapod Hive reduces maintenance.
When a ship becomes obsolete, you can opt to decommission it. This will return some BC and reduce maintenance. This should be considered carefully, since even an old ship may have some useful value either to add to the defense of an important location or just to act as a picket along one's borders so that enemy ships can’t sneak past.
A critical part of creating wealth is to minimize spending. For example, just about everything you build requires maintenance. A colony producing 100% manufacturing for ship building has no use for a research building, even if that building is sitting on a bonus tile. It should be destroyed to save the maintenance (and some other useful building substituted in its place). In essence, decommissioning ships that are out of date is also reducing maintenance, as mentioned above. On a larger scale, judging the size of fleets required for a given task is an important skill to learn so that one does not "overbuild" and spend maintenance for impressive fleets that actually are not being used.