Although primary, secondary and tertiary businesses are different, they usually cooperate to produce the products that we buy.
Goods move through a supply chain or the chain of production, which follows the formation of a good from extraction as raw material through to its final sale to the consumer.
In the given example wheat is grown and harvested on a farm / in agriculture (primary sector).
The wheat is transported (tertiary sector) to the mill/factory where it is grounded into flour (secondary sector)
The flour is then used with other ingredients (which also comes from the primary sector) to bake bread.
The bread is then distributed by road transport (tertiary sector) to the retailer / shop where it is made available for sale to the consumer.