I use  Windows OS and I want to install Ubuntu on another PC.

  1. Download software for bootable usb creation http://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/
  2. Download ubuntu image from http://www.ubuntu.com/download/desktop
  3. According to instructions from http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-windows install image on usb stick
  4. use usb-stick as bootable