Ususally usb drives show up as /dev/sda1 or /dev/sda2 need a number. To find out which dev node the drive is using (as root):
This will list both mounted and unmounted drives.
Then, just do a mount /dex/sdaX /mnt/usb
replace X with the right number.
You'll need a /mnt/usb folder obviously.
To simply the process add a line to /etc/fstab with the mount point you want.
Note: on some distros you need to be root to mount drives. I find this annoying so I add myself to the disk group in /etc/groups