Firstly you must include functions file called "functions.php" on source files like shown below:
?>include('db.open.php');
include('mbgallery/functions.php');
// Use functions below
...
include('db.close.php');
As it can be seen on above example firstly it's required database connection (with your created mbgallery database) then include functions in order for they to work properly with your gallery.
Go back to view MBGallery's functions via API Page.