copying files to disc

Hi
Can anyone help, I fairly new to computing and have been
trying to download some mp3 tracks onto my hard drive so
as I can then transfer them to cd.
I have managed to copy one track to cd but can not copy
any more. I keep getting messages saying "files ready to
be written to the cd", but when I click on " write these
files to cd" I get the message " the disc in the drive is
not a writable cd or is full"
The one track i've copied to the cd is only 44 bytes.
Also in properties what is meant be size and size on disc
as these two figures are different.