backing up files

hi. i need to backup some files on my hard drive and need to know what should i use for this. i need something that will backup at least 10 GB of space. i’ve heard of the CD/RW drives but i need to know more about them for example can u purchase these drives without having to install them inside your computer(sort of like an external modem). i would be most greatful to anyone who can tell me more information about this. thank you.