CDs can be used for sharing music, music videos, games, movies, etc. Any of these Needs to have their design be put on their CDs and their cases too. After designing the looks, you need to see how it would look on the CD and the CD case. This mockup makes your next job easy.
The design you have created now is ready to go on a CD. So choose the smart layer, add your design, then adjust the background and you are good to go. the rest is to show it to the client and see their impression on the job and you know it is going to be great.