You can set the maximum amount you're willing to pay for the item while using autobid. Autobid bids for you as other bidders increase the bid price. If another bidder outbids your maximum bid, you will be notified by email. But, realize that notification could happen minutes or seconds before the close of an auction. So if you really want something, you should bid the maximum amount you're willing to pay for the item when you make your first bid.
Bidding automatically ends when the auction does.
The high bidder and seller should contact each other within 3 business days of the end of the auction. It's a good idea to check your email or phone regularly after the auction. If you're the high bidder, and the seller can't reach you within this time, he or she may contact the next-highest bidder and sell the item to that person. Pay the seller promptly. You may make arrangements to ship the item purchased once your check clears.