ok...a CD-R is a blank disk, usually of a capacity of 700 Megabytes, which is like a one use CD. If you use the whole 750 megabytes, you can never put anything else on it again; However, if you use 10 megabytes, you can choose to leave it open for further burns, but you can't rewrite on the 10 megabytes
a CD-RW is a disk that you can use like 1000000 times. If you want to transfer files, its good for that; for example, you put 750 megabytes on it, and then transfer and then bring it back and ERASE the info of and then burn on the CD again. its usually called a re-writable CD, meaning u can keep on erasing and re-using the CD, as a pose to the CD-R which you can utilize the 750 Megabytes only once
Some car cd players don't recognize CD-RW, so it is mainly good for transfering stuff so you don't waste CD's or for making Backups; CD-Rs, which are cheaper and more commonly used, are used to make CDs, burn games, programes ...
hope that helped