Assuming it's an IDE drive it should be under /dev/hdb with a number for each partition on it. You have to mount each partition at a mount point, which is basically another file/directory in the filesystem. So if you used the command
sudo mkdir /mnt/second
We could create a directory to mount it in. Assuming it has only one partition, we can then use the command
sudo mount /dev/sdb1 /mnt/second
It should automatically recognise the filesystem and mount it there. You can now browse that folder which will contain the contents of the hard drive. This will only mount it for the session you're logged in, though. You need to edit fstab to make sure it mounts when you boot up. So:
sudo gedit /etc/fstab
Should load up Gnome's text editor with the fstab file. The contents already there should give you a good idea of how to enter it properly. First the device, in this example /dev/hdb1. Then the second column where you want to mount it, in this example we wanted to mount it at /mnt/second. Then type in the filesystem type, it should tell you what it was assuming it mounted successfully. Then add the mount options, and the dump and fsck options. For detailed options on these try reading something like
this since there's various options for you to tune it to.