China DOS Union

What command do I use?

What do you mean by how to use it?

You need to add a line like this to config.sys:
DEVICE=VIDE-CDD.SYS /D:MSCD000
Here, VIDE-CDD.SYS is your CD-ROM drive's driver file,
and /D:MSCD000 means using MSCD000 as the driver name.
And you also need to add a line like this to autoexec.bat:
MSCDEX /D:MSCD000
Here, MSCDEX is your CD-ROM drive's driver file,
and /D:MSCD000 means using MSCD000 as the driver name.

That doesn't work.
Mine is dual-boot, Win98 and Win2003.
I followed the steps above, rebooted, pressed F8 to enter DOS, and got a message saying MSCDEX cannot be recognized.

Of course, you must actually have those driver programs. It's not enough just to add those lines to autoexec.bat and config.sys.
You can make a standard Win98 boot disk and take a look at how it enables CD-ROM use under DOS.
Or you can download a boot disk made by wengier and see how it does it there.
Note: the CD-ROM drivers in a standard Win98 boot disk are oakcdrom.sys and mscdex.exe
while the ones in wengier's boot disk may be the vide-cdd.sys and mscdex.exe mentioned above.

You can load it manually; please refer to locdr.bat in my real-time Chinese-localized boot disk.