Most computers come with an internal CDROM drive. After inserting a disk, the CDROM can be immediately accessed through the directory /misc/cdrom, as the device is auto-mounted. It should automatically dismount if it is not accessed for a short period of time. You can manually force a dismount (e.g. if you want to eject the disk), using: umount /misc/cdrom.
Many, but not all, of the individual machines have CD writers. The easiest way to burn things to the CDROM is probably to find the menu items available through your window manager.
If this is not available, create a directory hierarchy that you want to be copied to the CDROM; the capacity of a CDROM disk is 650 Mbytes. Issue the command:
mkcd directory
to copy all of the files under the specified directory to the CDROM. This will take up to half an hour. The final step in the process compares the files on disk to those on the CDROM; if you see any error messages here, there may have been problems with the write (although sometimes you get errors here when everything is still fine).