Hooking up an external usb hard drive to the Raspberry pi is fairly easy. A hard drive plugged into a raspberry pi is /dev sdb.
You may want to format your external hard disk to be an ext4 filesystem instead of formatting it for windows.
Use fdisk and set it to make the whole disk as a primary ext4 partition. This will make your USB hard disk incompatible with Windows.
Format the disk
mkfs -t ext4 /dev/sdb
Make the mount point:
Add this line to your /etc/fstab file with sudo vi /etc/fstab
/dev/sdb1 /mnt/disk1 ext4 defaults 0 0
mount the disk
mount -t ext4 /dev/sdb /mnt/disk1
sudo apt-get install samba
Add this to /etc/samba.conf
comment = Samba server
read only = no
locking = no
path = /mnt/disk1
guest ok = yes
Reboot the RPI
You should now see the external hard disk on your windows network.