Buckingham Palace is the official residence of Queen Elizabeth II and his husband Prince Philip Duke of Edinburgh and the rest of the Royal Family. As a curiosity, you know that the Queen is inside the palace if the Royal Flag is waving on the roof of Buckingham
Apart from this use, the Palaces is the place where official acts and receptions are held in the United Kingdom. It is also one of the most visited landmarks within London and many visitors takes photos of its enormous front gates or watch the Change of the Royal Guard from outside these gates.
To know more about the palace, please click in the following link to an interesting article in Wikepedia