If you are buying your order will be placed in Bid list. If you are selling your order will be placed in the Ask list.
The highest Bid price will be placed at the top of the Bid list and the lowest Ask price will be placed at the top of the Ask list.
When a Bid and Ask price are matched a transaction will take place and it will the last traded price.
If you are looking to buy at a lower price, say $155.01, your Bid price will be placed 3rd in the Bid list, and unless the Ask prices fall to that level, your order will remain in the list until it trades, it expires or you cancel it. If prices don't fall to you Bid price you will not get a trade.
If you wanted your trade to go through you could either place a limit buy order closer to the lowest Ask price (however this is still not a certainty), or to be certain place a market buy order which will trade at the lowest Ask price.