Elected by the shareholders, the director or directors manage or direct the affairs of the corporation. Per state law, all regular corporations must have at least one director & most non-profit corporations must have three or more directors.
When a corporation is first formed, the director(s) is/are usually named in the articles of incorporation. If not, the incorporator(s) can either appoint or hold a meeting to elect one or more directors.
The director(s) serve(s) a term of usually one year or until the next annual meeting of shareholders. The corporation's bylaws describe the required number, term, authority, maner of election or removal and so on. With the annual meeting of shareholders, the director(s) can be re-elected for another term (per bylaws) or new directors can be elected. A director can also be removed by shareholders at either an annual or special shareholders meeting (again per bylaws).
Director(s) elect the officers of the corporation. At the initial directors meeting, director(s) elect the officers, adopt bylaws and authorize issuance of stock. Typically, the directors make only major business decisions and monitor the activities of the corporate officers. Again, their authority is more defined in the corporation's bylaws.