Newbie Question on adding private field

[AndrewQ]

Hi. I"m new to this and trying to figure out how I can go about adding a field that I only like to view in the BO. So which files should I edit for BO and also in the mysql. Say for example a field to store the cost price of the item I purchase or any private information about the item that is not for the public view on the Front-end.

Thanks. Any help would be greatly appreciated

edit: Is there some info or maybe my question does not clearly describe my problem. Any feedback?