how to know that HDD had detected

[cboys00]

i try to plug in second HDD in my desktop, how to know that the desktop had detect the HDD correctly

have any command to check it..thanks:)

[CSchwangler]

Is that HDD connected using USB? Then it should be automatically mounted and you would see a new desktop icon.
If you mean installing an additional HDD in you machine, you could, as root, use

/sbin/fdisk -l

to list installed HDD's and partitions.