"Shipping Address": Where you are sending your order.
"Billing Address": The address that is officially and currently linked with your credit card.
If these two addresses are different, then you must select "Use a different billing address" at checkout..
If you recently moved then your credit card is likely still registered with your old address for its "billing address".
Also, if you are sending your order somewhere else then your current home, then your shipping address will be different from your "billing address".
In both cases is is very important that you select "Use a different billing address" at checkout.