Well, you can use gparted, or the Gnome Partition Editor if you want to
use a GUI. It will look for hard disks, mounted or unmounted (it will
need to be unmounted to format) and you can partition/format from there.

I'm not at all sure how to use fdisk to partition from the command line,
but the command to format from the command line is mkfs, you can find
more info on that by typing:

man mkfs

At the command prompt.

Once formatted you'll have to edit your fstab file (/etc/fstab) to tell
Ubuntu where to mount the new drive and where to locate the new drive on
the system.

All commands have to be done as root to modify a disk.

Excellent documentation is here:
https://help.ubuntu.com/community/InstallingANewHardDrive

There is other cool stuff you can do with a 2nd hard disk, for instance
on my server I have everyone's home folders on a large hard secondary
hard disk, and backups on a third external hard disk. Leaving the main
disk for the operating system and swap space. This can be a waste of
space if you've got like 2 80Gb hard disks (or some other similar
situation). I still highly recommend keeping important user data on a
secondary hard disk.