If you bid Live, a 'Bid won' pop-up will appear. However, the winning of the bid must be confirmed by the auctioneer.
Shortly after the sale you will also receive an email with your invoice (specifying the lot's number, its characteristics, the hammer price, the additional buyer's fees).
If you have any doubts about winning a bid, please do not hesitate to contact the auction house offering the lot you bid on directly.