Adding on to a CD RW

Can you explain how to add onto a CD RW, to save files and then add to it? My old setup showed me how much space I had left, but with my new new does not,and I'm affraid that I will write over what is on the disk. The brand is unknown to me as it was installed in my Dell before I got it. Sometimes it says it needs to be erased, and I know its not full. any help would be great. I don't have a lot of smarts about this stuff...maybe to old to learn.

 

You need a special program to do this like DirectCD from Roxio, I believe.