I don't know if my answer to your question will be in the way you may be anticipating, but mostly, external hard drives (specifically their file systems) are mounted at /mnt. So let's say you have an external usb hard drive and it is situated in /dev as sda1. First, you would create the directory where it will be mounted to in /mnt...
Code:
mkdir /mnt/external_usb
* you can name it whatever you wish when creating the mount point. After its creation, mount the drive to it:
Code:
mount /dev/sda1 /mnt/external_usb
Then, enter it:
Code:
cd /mnt/external_usb
I hope this helps...