It allows you to boot your computer from a flash drive that has a pre-installed Distro or App on it.
Your computer needs to both boot from USB and recognize the flash drive as a USB Hard Drive. You will need to access your Bios and set it to boot from the USB port.
UNetbootin can either use a supported distro ISO file that has been saved on your hard drive or you can select a distro from the drop down box and it will download and configure the flash drive for you.
Suported OS: Windows, Linux, OS X (Mac)