Not all pharmacies work with Blink Health. Some big ones like CVS, Rite Aid, and Walgreens, for example, do not participate and will not honor a Blink Card as payment.
You can find a list of participating pharmacies in your area here: https://www.blinkhealth.com/pharmacies
Once you have a prescription sent to a participating pharmacy, you will tell the pharmacist that you are not using insurance, and that you plan to pay with a Blink Card.
You can find your Blink Card here: https://www.blinkhealth.com/account/blink-card