First let me say that I am new at MySQL / PHP.

I have a list of categories(18-20), each having sub-categories(15-40 / category). Also I have a list of headings from the yellow pages (about 4900).

I am looking for guidance about how to set the database up, and how to allow the classified ad author to use the db to assign category / sub-category / headings. Any suggestions would be appreciated.