The main function of the British Royal Guard (Queen's Guard in English) is to ensure safety, although its performance is usually limited to ceremonies. In London, the changing of the guard at Buckingham Palace has become one of the main tourist attractions, because the change is performed accompanied by a marching band. You have all the information in: «Queen Elizabeth II of England and the British Royal Family«.
You have all the information in: "Queen Elizabeth II of England and the British Royal Family".