The outbid is done by bidding alot more than the bid. Like say last bid shows 125, but that person may have bid 500, so each time someone else bids...say 150, it looks original bidder just outbid you, but they put in hign 500 in first place. GIN is Get It Now...price. That is what seller will take for right now. Then bidding stops & person who puts it that amount is the winner.
You set your max bid and if someone else's bid is lower than that then it will automatically out bid them until they set a bid higher then your max bid. And GIN is "get it now" it means that the seller has set a price that you can pay without bidding and it will automatically end the auction. :)