With a rewards credit card, you get a percentage back of what you spend, typically in the form of cash back, points or miles. You can redeem this earned currency through your card provider's rewards portal. These points and miles represent a certain value in cash which can range depending on the rewards program.
For cashback cards, rewards are usually expressed as a percentage. If a card offers 2% cash back on all purchases, for example, you'll receive $2 back for every $100 you spend.
For other cards, rewards are usually expressed as a point or mile multiple. A card might offer 2x points on all purchases, for example, which means you'll receive 2 points for every dollar you spend.