Directors are officers of the company who are responsible for managaging the company and making the decisions as to its operation on a day to day basis, for the benefit of the shareholders. A private company must have at least one director and a PLC must have at least two.
Certain important decisions, eg to change the company's name have to be made by the shareholders at a General Meeting, however most decisions will be made by the directors.
Directors have to abide by a number of duties which are set out in sec171-177 CA 2006, and include duties such as to 'promote the success of the company', and 'exercise reasonable care,skill and dilligence'. Other responsibilities which directors have include responsibility for notifying Companies House of certain changes, eg to registered office, appointment of directors etc., and for registering the annual return and accounts.
The same person can be both a director and a shareholder, and this is usually the case in private companies. On the other hand, a director need not be a shareholder or vice versa.
Please see the links below for further information on Directors: