Ensure that the front of the money order has your name in the Pay to Order Of field. In many cases, the purchaser of the money order will complete this field. If you must complete the field on your own, be sure to enter your legal name. Endorse the back of the money order. Present the signed money order and a valid photo ID to the post office representative in your area. The photo ID can be a state issued driver's license, state ID, military ID or passport. Wait to receive your cash back from the money order. There is no fee for cashing a postal money order at the post office.