To mount an external HDD or PenDrive (USB Flash Drive) simply type this Command in terminal

Create a Folder where Files to be mounted example we want to mount the file under /home/tommy/Desktop/Exhdd

$ mkdir /home/tommy/Desktop/Exhdd

$ mount /dev/devicename /home/tommy/Desktop/Exhdd

device name can be found using this command below

$ fdisk -l