You must first be a registered member. Once you have registered simply login to your account and click on the "Sell" link. The first thing to do is select a general category for your item, note that you can choose a more specific category further into the listing process. You can then enter in your chosen settings and item description
To place a bid on an item you must first login to your account. Once logged in a bidding box will be displayed at bottom of all auction pages. You can use this box to place you chosen bid