A market order is a buy or sell order to be executed immediately at the current market price, in which the client only needs to put the total to spend.
For example, you want to buy BTC with 5 USDT at market price.
You can choose BTC/USDT pair to make a buy market order.
Just put how much USDT you want to spend (5 USDT), then click on BUY BTC to confirm your order.
The order will be executed immediately at the market price and you can find the details in Orders history.