The amount of rent depends on the size of the retailer's warehouse. A retailer that does no business still has to pay rent and will eventually go bankrupt. The producers, retailers, and consumers have fixed locations and cannot trade directly. They rely on trucks to ship goods from one place to another. A truck can buy crates from a producer and sell them to a retailer, or it can buy units from a retailer and sell them to a consumer, or it can do both.
Trucks can move around the country, using gas.
The country contains several gas stations at which trucks can buy gas. A truck that does not trade will eventually not have enough money to buy gas. A truck without gas is stuck and can do nothing. The objective of the game is for retailers and trucks to trade in such a way that there is a steady flow of goods from producers to consumers. Since the game is simulated by computer, the actual objective is to write code for a retailer or truck.