Method:

1. login on the web not app.
2. Click on Rewards and apply the coupon before you go.
3. Go into the store and at the register give them the phone number associated with the account and it automatically takes it off the purchase.

100 points = 1$ cash off at checkout

or can be used in their rewards page for other offers aswell

And for gas

100 points = $0.10 off/gal, up to $1.00 off /gal