'Qty' or quantity is the number of business card prints you desire to purchase. 'Single' and 'Double' refer to whether your business cards are printed on one side or both sides.
Please note that if you wish to have two different business card designs then they constitute to two separate orders. For example if you wish to purchase 1000 business cards for your business and 1000 business cards with a different design, then you need to purchase two separate lots of 1000 business cards. You cannot purchase 2000 and then have different designs printed on half of them.