BILL=SHIP means when you putting address in checkout page
you must need to add same address in both Billing and shipping address -
For example if you are carding product "ABC"
and you are in checkout page so you need to add details of Billing and Shipping same ..
And the address will be your receiver info where you want to received the item
In short : BILL = SHIP (You add you receiver real address in both - No need to use CC billing address)