JCPenney Credit Card rewards?

I was shopping in JCPenney earlier, and when I got to the checkout, the cashier asked me if I wanted to apply for one of those credit rewards cards. I wasn't too sure, so I said no. I've never had any credit cards before, only a debit card. I guess my question is, what exactly does it do? I know it's a card where you can only use it in the store, but do you get like, rewards on it for spending a certain amount in the store? Also, she told me that I wouldn't get charged any annual fees. Is this true?