Back up issue

I set up which files to back up. This worked ok the first time, but when I chose the same back up file the next day before I left, the system seemed to copy the previous back up - hence no changes were made to my CD. Do you have to create a new back up file each day or is there a way to tell the program that you always want to back up the same folders each time on a manual basis. I would hate to create a new back up file each time I want to back up.

Thanks for the help - anyone!