There are primarily three different types of coupons that can be used at the grocery store.
Manufacturer Coupons
These can be found in national coupon inserts in newspapers, direct-mailers, magazines, package inserts, online, through surveys, mail-in forms, and often accompany samples that you receive in the mail. Usually the manufacturer will pay the face value of the coupon directly to the store.
Retailer Coupons
These are coupons that retailers will post in their store newspaper ads, through direct mail, or in local newsletters (subdivision or area newsletters). Usually the manufacturer offers an advertising allowance to the store to cover the expense of the advertisement and mailing fee.
Online Printable Coupons
Often manufacturers and grocery stores will have coupons listed on their Web sites which can be printed and used in stores.