To use this feature you must be a registered user. After logging on select the item you would like to purchase. You will see tabs next to the Description tab:

If the auction has a BIN (BuyItNow) and you agree to that price then select the BIN tab:

Click the BuyItNow. The AuctionSite will send a message to both parties. From that point it is between buyer and seller if cash, paypal invoice, etc. If the item does not have BIN and/or you'd like to make a bid on an item select the BID Now tab:

Enter the bid amount, or Maximum BID if Proxy bidding (select check box if proxy bidding). Similar to  the proxy bidding system used by eBay, where the winner pays the lesser of their actual bid and the second-highest bid plus one bidding increment. Proxy is your max bid. Let's say the item start bid is 30$, you Proxy bid $40.. If there are no other bids you  get it for $30. If someone bids $35, it will automatic increase your bid to $36. The next step is to wait to the end of the auction. You  will be notified of the progress, if someone outbids you, you win, etc.