You can't unless it has has a 'buy it now' option, obviously you will have to pay the 'buy it now' price and not bid price if you really wanted to buy it now!
If you want it for the bid price, you put in your bid on those items, wait for the auction to end and hope your bid is the highest bidder.
You can't purchase a bid only item.......................... There will be very few sellers if a buyer can buy the item at the (typically low) bid prices...haha.
