Your ticket should have the booking conditions printed on it (this will often be in shorthand, such as "NONREF" for "non-refundable"). Some tickets are refundable, some are not. With some tickets you may be able to use the return coupon at a later date, or exchange it for an MCO (Miscellaneous Charges Order) which is a voucher that can be used towards future bookings. It all depends on the kind of ticket you have.
If there are no booking conditions printed on the ticket ask the airline what the conditions are.