Note that resulting USB drives are bootable only on PCs (not on Macs). Microsoft Windows 2000/XP/Vista/7, or Linux, or Mac OS X 10.5+.iso file if you've already downloaded one or your preferred distribution isn't on the list.
You can either let UNetbootin download one of the many distributions supported out-of-the-box for you, or supply your own Linux. UNetbootin allows you to create bootable Live USB drives for Ubuntu, Fedora, and other Linux distributions without burning a CD.
