To get coupon codes for Global Airport Parking, go to its website and find the airport you need to use. Coupon codes are not generally applicable at any Global Airport Parking service, and can only be used at the specific airport to which they apply.
Navigate to the Global Airport Parking website, then click the Coupons link at the bottom of the page. This takes you to an airport listing that is sorted by alphabetical order. Find the airport you plan to fly through, then click the link to its specific page. On the airport's page, you find a graphic display on the right. This lists the amount of the discount, and the code you apply when ordering your parking in advance.
To apply the code, use the search menu on the left to input the day and time you are using the parking service. If Global Airport Parking has halted service to that airport for any reason, you are notified. If you are able to make a booking, click the Reserve button for the parking location you need. These locations are typically close to the airport you use. On the Reservation Checkout page, apply the code you received when you first arrived on the airport's page.