Each order will be assigned a unique reference code that will be used to identify it both for the user and exchange staff.  

Order IDs can be found on the Orders Pane of the Trading Page, they are on the left side of the Open Orders, Order History, and Trading History tabs. Clicking on the Order ID will copy it to your clipboard so that you may easily refer to specific orders should you need to contact support.

How do I find my Order ID?