To redeem points you'll need to make sure you have an account with that store and that you're logged into your account.
There are two ways you can redeem, within the Smile panel & at checkout (store permitting).
Redeem within the Smile panel
This video walks you through the steps to redeem:
Redeem within the checkout
Some stores may have the option to redeem your points at the checkout (incase you forget to while you're shopping!) Here's how you can do that:
FAQ
I redeemed this coupon by mistake! How can I undo this?
You will have to contact the store's customer support and they should be able to cancel the coupon and refund the points
How can I redeem more than 1 coupon at a time?
You can check out this article and it explains a little more