A Market order is an order which is executed immediately and filled at market (i.e. the first available market price). This type of order is used by traders when immediate market entry/exit is the main priority. It is important to note that market orders are filled at the first available market price, thus they are subject to market slippage (the difference between expected price and actual fill price)
Order size USD - reflects the full size of your order taking into account selected leverage. An amount equal to the margin cost for a position is reserved on the Wallet balance immediately upon opening a position.
When placing a Market order, you will need to select the order size. Once you confirm a market order, it will be immediately executed and filled at the first available market price.
Margin cost - the amount of personal funds which are required and reserved in order to open a position.