jiml8's way could be the proper way to get a USB pen drive detected and mounted but in Ubuntu that is what would happen if you
drop everything temporarily leaving the screen showing nothing but just the desktop, plug a USB pen drive in and in less than 15 second you should see it mounted automatically and show up in the desktop.
Mine did just that in 10 seconds.
Equally if I want to remove it (Ubuntu mounts as /media/1GB BACKUP) I type
sudo umount /media/1GB BACKUP
and it will disappear in front of my eyes.
My experience is modern kerenls will repeatedly scan the USB ports and detect any attached device "automatically". Whether the USB device would be mounted automatically depends on the distro and also on a previous device names exist in /mnt or /media directories.
The "fdisk -l" of my post #3 is a confirmation that it has been detected as a piece of hardware and given a device name. Say if the USB device is a raw hard disk it will "always" be reported in "fdisk -l" but cannot be mounted because it has not been formatted and has no filing system for mounting.