If you're going to use a credit card, you might as well get something out of it. Rewards credit cards give you a small kickback for making purchases with that credit card. Not all credit cards give rewards and not all consumers qualify for rewards credit cards.
The prospect of earning cash, points, or free flights for something you'd have done anyway sounds attractive, but be careful because rewards cards can lead to debt. Since interest rates on rewards cards are often higher, it's better to pay your balance in full every month. Otherwise, you're funding your own rewards with finance charges.
Some rewards cards are cleverly promoted making you think you can earn more than you actually can. Before you send in your application, check out reviews of the rewards card you're considering to see if it's really a good deal.