I have 5,000 free miles from a giveaway does this mean..?

You are interpreting this certificate the wrong way. It is used in an airlines frequent flyer mileage program. It is not good for 5000 miles of air travel, but can be used to get mileage credit for the airline it's good on-- For example, most airlines give you a free ticket after you've traveled 25,000 miles on them. You now have 5000 of those miles-- Now just travel another 20,000 paid-for miles on the airline, and presto! A free trip is yours!