Buy the ask & Sell the bid

Buy the bid and sell the ask is a term that you will hear a lot, traders use it when they are trying to get in on a trade immediately. It's just like doing market order but with a market order, you have the disadvantage of getting fills at a totally different price than intended.

If you are selling a stock, you are going to get the bid price, if you are buying a stock you are going to get the ask price. The difference (or "spread") goes to the broker/specialist that handles the transaction.