The term "Creole" refers to cultural elements that have resulted in the mixing of early colonial cultures, particularly those in the Louisiana/Mississippi region because it was an area where French and Spanish settlers were close enough for regular interaction, and the mouth of the Mississippi and Gulf Coast were areas of major trade and commerce. This meant cultural influences from many other places as well (Africa, the Caribbean, etc.).
The term Cajun refers to French Canadians who were kicked out by the British and later settled in southern Louisiana.
Cajun food tends to be simple and rustic, utilizing local ingredients. There will likely be a rice. It uses roux and heavily seasoned stock, onion/celery/carrots (traditional French) with the addition of bell peppers, and often wild game, smoked meat, or seafood (sometimes multiple meats).
Creole food reflects mixed heritage. It contains elements of a wide variety of cultures, including Cajun. That's why the two are so similar. But you can expect Creole food to include much more far-reaching ingredients and flavors because of the African and Caribbean influences. One might consider Creole food to be (typically) more refined and elegant, though not always.
As another answer said, you can expect to see Creole food more in the New Orleans region, because it was a port, which is a natural mixing area for different customs, while strictly Cajun food will be more prevalent in the Bayou because that is where the Cajuns settled after leaving Canada.