Depending on the device you are using it will be different. That being said, In most cases including using a computer you will insert the CD. Then go to my computer and highlight the device playing the CD and RIGHT click on it. You will see an option that says "format". That will erase all data on the CD (as long as it is not a CD-R) and you then have an empty CD. CD-R's cannot be erased once loaded.
Hope this works for you.