GIN means Get it now. the GIN for the gameboy is 10,000 credits. If you use the GIN option that means you dont have to wait for the 9 days to go by and have to worry about losing to someone that bids higher then you. Its kind of like the Buy It Now option on ebay.
Its the Gameboy start up screen on the last picture just so people know that it is in working condition. And i forgot to mention on the other reply i think you can use normal batteries in it from what ive read online but ive never taken the battery cover off to see. Im pretty sure you can pick up a charger for it for fairly cheap