A Data only CD (MC style), is a CD on which you can put one data track. You are able to select files and folders you want on the CD in a Midnight Commander way.
The usage of the Data Only CD is simple. From the left filetree you can drag files and directories to the right filetree, which need to be added to the project. With the Calculate ISO-image size button you can calculate the size of the image.
When you are finished, you can click on the Write CD button to start burning your CD.