There are 2 types of coupons, Manufacture and Store.
Manufacture - You can use at any store that accepts coupons
Store - You can only use at the store printed on the coupon
At most stores you can (stack) use both store and manufacture coupon at the same time on the same purchase.
Example: If you have a Walgreens store coupon for $3/1 Abreva and you have a manufacture coupon for $3/1 use both and you will get $6/1 all together for that purchase. Match that with a sale and there you go.
Check with the store coupon policy to see if they do allow stacking. Its always good to print them off and carry them with you.