Answer:
Put quite simply, it is now a popular museum devoted to showing people from around the world where Anne Frank lived, and what it was like. More than 50 years ago, it was where Anne Frank and her family, the van Pels, (van Daan in Anne's diary) and Fritz Pfeffer lived, for more than 2 years, in a cramped area in the back of the house, hidden by a a door disguised as a bookshelf. Downstairs was an office where Anne's father had worked, and the refugees had to hide away and avoid capture, as they were Jews and would be sent to concentration camps if found, which, sadly, they were in the end.