can someone tell me why i'm getting an error whenever i try using
A: or CD ROM? or even tell me how to use it.

Be more specific, what are you trying to do? I suppose you want to access your CD-ROM and floppy and you are trying to use DOS commands - guess what, linux ain't DOS, for linux to see the contents of your CD-ROM you must mount CD-ROM first. Issue as root in Xterm or Konsole or whatever terminal emulation you are using:
mount -tiso9660 /dev/cdrom /mnt/cdrom
for this to work you must make certain that /mnt/cdrom exists on your system and /dev/cdrom is pointing to the actual CD-ROM drive, if you are new to linux I suggest getting a linux book that covers using linux, or search the net for linux to see what it can offer.

In Linux everything is a file. The same with drives, cdroms, floppies etc. To have access to any of them you need to mount them (using command "mount"). In most modern distros the commend neo7777 gave can be used in simplier form:
mount /mnt/cdrom
for cdrom. After running this commend (from console) you'll have contents of your cdrom into /mnt/cdrom directory. There's also similar command for floppy:
mount /mnt/floppy

The /etc/fstab also plays a part.

Right, but in modern distros it's set up by default.