I guess this a fresh hdd you've installed. You'll have to partition it and then format it with the filesystem of choice.
You can partition it using cfdisk:
Then, format it with the partition of choice, eg reiserfs:
Code:
mkreiserfs /dev/hdc1
This will format the first partition on the disk.
You can then mount this on a mountpoint, or add the disk to /etc/fstab to make it mount on boot.
You'll have to be root to do all this.