The Galileo board doesn’t have an interface for a display. The only way to access the board and get a “visual output” is through the console which can be accessed through the serial port as it is shown in the following document: Intel® Galileo Boards and Kits — Console Serial Cables
The Yocto image is the one supported by us, and it can be downloaded from the following link: http://downloadmirror.intel.com/24355/eng/SDCard.1.0.4.tar.bz2. If you want to use Debian instead, I recommend you to visit EmutexLabs. They offer an image called Ubilinux which is based on Debian.