Credits can either be purchased or given to you when an event ticket is canceled.
When you are issued your credit you will get an email where you can view your credit balance and credit I.D.
This credit I.D. is much like credit card number, you can use it when placing an order or you can give the I.D. to someone else and they may use it for products or events.
If you don't know your credit I.D. you can contact support and they will be happy to get it resent to you.
You can reach support at 866-760-8255 or firstname.lastname@example.org