RW stands for ReWritable. With a CD-R you can't put anything on it more than once. You add songs to it once and that's it. It is how it is, you can't do anything else with it. I prefer to get a CD-RW...
A CD is a read only disk. CD-R is a recordable disk meaning writeable but only once up to the capacity. CD-RW- allows you to rewrite over old data with new data, many times.