SAVINGS AND EDITING FILES ON CD'S

I don't understand the concept of writable cd's. I need
to be able to save & edit files on a cd because I take
work home almost every night, and the editing that I do
on my spreadsheet & Documents I need to be able to bring
up at work the next day. Every time that I save a doc. on
a cd then I bring it to work it says that it is a Read
only, I thought that CD-R and CD-RW was able to write and
save and retreve a doc. so that you could transfer data
to another computer using a CD. I have a new VIAO 4 with
a DVD-RW/CD- Drive & a CD-ROM Drive at work. What am I
missing?? HELP