You can't get 'cashback' in supermarkets, etc, with a credit card.
You can withdraw cash from an ATM but:
(a) you'll probably have to pay a transaction fee ;
(b) the interest rate on cash advances is usually significantly higher than on card payments ; and
(c) there's usually no 'interest free' period on cash advances, so interest is charged from the moment you withdraw the money, rather than from when you receive your next statement.
If you need to use your credit card to fund day-to-day living expenses (such as supermarket shopping) it makes more sense to simply pay for your shopping with your credit card, rather than to withdraw cash to use for your shopping.