First, you have to select an online auction house. With more than 1,000 of them to choose from, it's really a matter of finding a site you can trust and are comfortable with. The bidding process is straightforward. Register with the site, surf around until you find something you like and then bid away.
Specifics vary from site to site, but auctions generally last from a few hours to several days.
You might be one of only a few bidders or, if you're after a hot item, you could find yourself in an all-out firefight. All you have to do is negotiate payment and delivery terms with the seller. Well, not quite. There are a few issues to consider when using online auction houses, not the least of which is fraud. Find out what others have to say by visiting chat rooms or the site's feedback forum.