Financial accounting is a specialized branch of accounting  that keeps track of a company's financial transactions. Using  standardized guidelines, the transactions are recorded, summarized, and  presented in a financial report or financial statement such as an income  statement or a balance sheet. 
Companies issue financial statements on a routine schedule. The statements are considered external  because they are given to people outside of the company, with the  primary recipients being owners/stockholders, as well as certain  lenders. If a corporation's stock is publicly traded, however, its  financial statements (and other financial reportings) tend to be widely  circulated, and information will likely reach secondary recipients such  as competitors, customers, employees, labor organizations, and  investment analysts. 
It's important to point out that the purpose of financial accounting  is not to report the value of a company. Rather, its purpose is to  provide enough information for others to assess the value of a company  for themselves.
Because external financial statements are used by a variety of people  in a variety of ways, financial accounting has common rules known as accounting standards and as generally accepted accounting principles (GAAP).  In the U.S., the Financial Accounting Standards Board (FASB) is the  organization that develops the accounting standards and principles.  Corporations whose stock is publicly traded must also comply with the  reporting requirements of the Securities and Exchange Commission (SEC),  an agency of the U.S. government.