The bird's might take few days to few months to use the nest box as it's a natural process and depends upon the presence of birds in your locality and the bird nest box is not a magnet which will attract birds from far and wide
Do not change the place frequently and install it within climbers or shrubbery on a wall or on tree
A traditional and versatile bird box that can be placed in any garden your window grill, balcony or backyard installing it is as easy