Businesses earn you Coins; coins allow you to buy more abandoned buildings, which you can then turn into either Housing or more businesses, which then allow you to earn more coins. The great circle of life.
Each business stocks three Products you can sell, and each product needs a Survivor to stock and sell it, and each yields increasing coin amounts, and also costs more in terms of both time and Supplies required to build it.
A business has a particular Personality that it's favourable to (these are indicated by the colour of the name label when you select a business to build), and assigning workers to a business whose personalities match will yield a 50% higher return on the number of coins on the product that the survivor is producing. Most of the time, these personality matches are fairly logical; for example the casino is favourable to the "Dreamer" personality, and the target practice range is favourable to the "Warrior" personality.
Product selling happens in two phases: first, you need to "stock" the item, which consumes Supplies and takes some number of minutes/hours to complete, then one stocked you can "sell" the product, where you begin earning the number of coins the product is worth gradually, until it runs down to zero and then you start the process over again.
Coins accumulate according to time "ticks" in the game. A "tick" is approximately 8 seconds. A level 1 product will yield 1 coin per tick, a level 2 product will yield 2 coins per tick, and a level 3 product will yield 3 coins per tick. So if all products are stocked within a business, you earn 6 coins per tick. Once you've received all the coins for a product, you need to re-stock and begin again.
The number of supplies needed to re-stock are higher the higher the coin yield from a product is. However, higher-level survivors will apply discounts to the amount of supplies needed, equal to their experience level value. For example, a level 9 survivor, a level 5 survivor, and a level 3 survivor would earn a 17% discount (9 + 5 + 3) on the amount of supplies. There is no way to increase the base level of a survivor at this time, so it's recommended to evict lower-level survivors to make room for higher-level ones.