Basically with market order you are showing that you will sell or buy stocks at the best available current market price.
Market Order is best for the “buy-and-hold” investors. Because the for the “buy-and-hold” investors the small differences in price are less important than to those who are day traders let’s say.
A market order doesn’t put a price parameters on the trade will lead to your order being executed immediately and fully filled. Unless of course you are truing to buy a million shares and try to takeover the coup.
However don’t be too surprised if the price you will relieve or pay won’t be the exact price you were quoted just seconds before.
Both the bids and asks prices fluctuate constantly throughout the day. Which is why the market order is best used when buying stocks that don’t experience wide price swings.