hi,
root as the super user root(this is not regular user root).
for the usb device question , Linux from the 2.6 kernel sees your disks as /dev/sda, /dev/sdb , /dev/sdc etc . so when you plug your usb memory it will see it as /dev/sdb(if your already present hard disk is seen as /dev/sda ...).
you need to know how your usb flash memory is seen before formatting because if you make a mistake and format your hard drive you will be in trouble.
to see how you usb memory is seen just run the following command as Felarin said
(its a small L after the - sign)