Discover credit cards offer a unique new customer incentive.
Instead of a fixed reward for a certain amount of card spend (IE: earn $500 for spending $3,000 within 3 months), Discover instead doubles the cash back or miles you earn within your first year, in a program they call Cashback Match (or Discover Match, for the travel card).
For both programs, you'll be automatically enrolled when you open your new credit card account.
There's no maximum to how much of a match you can earn. Simply spend using your new card, and all of the cash back or miles you earned within that first year will be matched within 2 billing periods after your anniversary.