From the announcement:
How it works:
• All orders placed with Forge World between 00:01 (GMT) 11th November 2013 and 23:59 (GMT) 20th December 2013 will receive a free Standard Shipping voucher within the order for use on a future order.
• Free Standard Shipping vouchers must be redeemed before 18:00 (GMT) Friday 31st January 2014. There is no limit to the number of vouchers that you can collect or use.
• To redeem your voucher please call the Forge World Customer Services team on 0115 900 4995 (UK), 011 44 115 900 4995 (US) or 0044 115 900 4995 (Europe and Rest of the World).
• Please have your voucher number and the number of the order with which you received your voucher to hand – you will need both of these to take advantage of the offer.