1) You can't mount a harddrive (except in rare cases, where the drive is basically just one big partition)
2) You need to specify a mount point if you're using the mount command
Now, if you don't have any partitions (e.g. sdb1, sdb2, sdb5, etc) on the drive, you'll need to make one (unless your drive is one of the rare cases I mentioned above).
sudo mount /dev/sdb1 /mnt
Hpefully this points you in the right direction and you can sort your self out from there, but if you're still struggling to understand why you can't mount it, post the output of: