Market orders are transactions meant to execute at the present market price. It buys or sells as quickly as possible to available limit orders currently sitting on the order book.
With a Market order slippage may occur. This means that you get a slightly higher price with a buy market order or slightly lower price with a sell market order. In very volatile times, slippage can be substantial.
You can choose to set a market buy or a market sell order, and you will have to pay a fee for your transaction; the so-called 'Taker Fee'.
Example: Suppose you hold a Bitcoin (BTC) balance in your Bullex account and you want to buy Ether (ETH). In order to do so, you go to the trading page for the ETHBTC pair. Under the chart you click on the tab 'Market order' and you fill in the amount of Ether you want to buy. The system automatically fills in the going Market price. If you agree with this price, and after doublechecking your order, you can click 'Buy'.
Please note that it is not possible to undo and/ or reverse a Market order.