Producers spend money for land, buildings, machinery, resources, and workers. Money circulates through the economy as producers pay owners of land, builders of buildings, makers of machinery, sellers of resources, and a labor force. Products, when they are sold, circulate money back to the producers to keep production going. The money that producers use to start a business comes from investment. Investors believe that a product or service will have a good chance of success, so they want to put money into a business.
Some people invest by buying stock, which is ownership in a company.
Others invest by making loans buying bonds issued by the company. Once a business is operating, it gets the bulk of its funds for future growth and continued operations from borrowing. Getting investment money together is the start of a process called capital formation. Investment money is the initial capital. The source of investment money is savings.