You know those coupons that mysteriously print out at the register after you have completed a transaction? These are called catalinas. These are perhaps the most confusing types of coupons to use. I am still not an expert at using them. I think I have only effectively used them once. (here) Some catalinas are for a specific product (ex: save $2 on 5 boxes of General Mills cereal) and some are good to spend as store cash (ex: save $7.00 on your next Albertson's purchase).
Because I am not an expert at these, I will refer you to someone who is!
Fabulously Frugal: Catalinas