desertgrandma has the right of it -- you can change the metadata.
My assumption is that you want calibre to get it right in the beginning, or at least closer. To help you, we need more information.
- What kind of books are you adding? By that I mean what format (epub, mobi, pdf, txt), not what genre.
- What version of calibre are you using? On what operating system (Windows, Mac, etc)?
- What is the setting of the preference 'Read metadata from file contents rather than from file name'? (preferences -> adding books)?
- If the preference 'Read metadata ...' is unchecked, then what is in the 'regular expression' box? And what do your file names look like? (A real example would be best.)
Ball is in your court.