As mentioned above that is Odin mode, aka Download mode. Essentially you can flash firmware to your phone through this, updates, ROMs...quite a few different things can potentially be flashed through it. Kinda similar to .sbf if you are familiar with the Motorola line, although this is different at the same time. I am not sure if it will be useful for the SGN though.
You can get there by holding volume down while powering on.