At the order screen the settlement option function will give you the ability to choose which currency you would like your payment to be taken from if the total amount is not available in the currency of the instrument you are buying. This can be selected by clicking on 'Show Settlement Account'. To change the preferred order of the settlement currency, simply drag the currencies in your preferred order.
Ensure that the Advanced Mode, and Order Preview toggle are enabled, to review your order prior to it being sent to the exchange. Thus allowing you to amend the order or else proceed with the transaction.
Your Order will then be placed, becoming visible in the “active orders” section. You can click on the arrow in the Active section in order to View, Modify or cancel your order until your order is executed.