A USB storage device plugged into the system usually mounts automatically, but if for some reasons it doesn't automount, it's possible to manually mount it with these steps. Albeit there are many different ways to accomplish this. At the terminal as root, type:
fdisk -lmkdir /mnt/usb_drv
This will give you information concerning the name of the usb device "/dev/sdx", also the type of filesystem format (ext3, ext4, hpfs/ntfs, etc.). You can the use the mount command or pmount. When using mount you must create a directory to mount the drive to.
mount /dev/sdxx /mnt/usb_drv
pmount /dev/sdxx /media/usb_drv
pmount will create a temporary directory /media/sdxx and mount the drive to that dir.
To double check, the command:
will give you information on all mounted drives.
When your finished with the drive:
which will unmount the drive and if you've used pmount to mount the drive the temporary directory will be removed.