They choose the supplies they purchase, which employees they hire, the products they sell, and where they sell those products. They use their skills and resources to create goods and services that will satisfy existing and prospective customers.
One of the main reasons why I have always wanted to start my own business was for this exact reason. Business owners and managers have such a big control over everything and they get to get their hand dirty with everything. They get to be apart of everything when it comes to who their hiring to what their selling.