These related Help pages may answer your question:

• What do I need to know before I bid on an item?
  eBay members find bidding and buying on eBay to be both fun and a great way to find bargains. Before you start bidding, take a moment to look at our overview of bidding and buying by clicking the link above . . . .
• How does bidding work on eBay?
  eBay uses an automated proxy bidding system. You enter your maximum bid, and eBay bids for you an amount just high enough to beat the reserve price (if the seller has set a reserve) or to beat the high bidder's maximum bid, whichever is higher. Your maximum amount is kept confidential from other buyers and the seller. No bid will be placed for you that's higher than your maximum bid. Click the link above to learn more about the bidding process and see examples. . . . 
• How do I contact a seller?
  You can click the "Ask seller a question" link on the seller's item page or email the seller from the email address provided in the "End of Auction” email. If you've completed a transaction with the seller, you can also click the "Advanced Search" link below the "Search" button at the top of most eBay pages. Then click the "Find Contact Information" link on the left side of the page. . . .