If you compress your file(s), you can enter the volume size in the
"Split to volumes" field in the "archive name and parameters dialog:
general options" to create volumes (multi part archives).

By default it is entered in bytes. But if you add a lowercase letter 'k' at
the end of the volume size, the entered value will be considered as kilobytes
(multiplied by 1024).
Use an uppercase 'K' to denote thousand of bytes (multiply by 1000), '
m' means megabytes and 'M' - million of bytes.

It is also possible to select the volume size from the list associated with
this item. Note that if you are archiving to a removable disk, you may select
"Autodetect" from the list and WinRAR will choose the volume size automatically
for each new volume.

For multiple CD's you can enter for example "700m"  for 700MB CD's.
WinRAR creates a multi-volume archive (volname.part001.rar, volname.part002.rar, etc. ) The volumes are 700MB and the last volume may be smaller.

After this, you can burn the volumes on CD.

Some burning programs have a special test mode, with which you can determine
the maximum capacity of CD blanks, so you can enter the maximum size for the volumes.

To unpack volumes you need to start extraction from the first volume.
Select "Process all files in all volumes from the current" in the menu that appears.
If volumes are stored on non-removable media like a hard disk,
you need to put all volumes in the same folder before starting extraction.

To repack a single rar/zip/tar/... archive into multi volumes archives, please
use the the convert function available as of WinRAR 3.10.