you bid on the item; you can click on "add to watchlist" if you want to keep up with the bids since this is a long auction; you have your watchlist over in your left column on your home page; most people like me wait until about an hour or two before the end of the auction before they bid. good luck!
A seller can offer a GIN (Get It Now) price, so the buyer can just purchase an item immediately, but I can't do that now because once somebody put a bid on an item, the rules say you can't enter a GIN. is that what you were wanting to know?