Be seen by customers at the moment they're searching on Google for the things you are offering. Coupons can only be used on new accounts, one per account, and they do not work with invoicing or manager-defined spend and expire after a single use. To existing users with adwords accounts, these discount codes need to be used with a new ad account. Google is constantly adding new codes, discounts and sales landing pages, get your Google Coupon Codes
For more detail, click on the following link.