CD Modes/Types?

Hello,
I have a SCSI CD-ROM Drive and have burned a few things. I noticed there are many terms I don’t understand about CD RW. There are “modes” which I have no clue about. Multi-Session CD’s which I know nothing about. I still don’t know if you can have data and music on the same burned CD. Is a CD finished once you make it “closed” which I don’t really know anything about. Can you write back on it after it is closed or is it trash after that? I am using a good program called Nero if anyone out there is looking for a good CD burning program to use. They offer a free full option trial version on their site. www.nero.com
If someone could answer those questions I’d really appreciate it.