Sprint is an ability on Spore. It makes your creature go faster and helps you get to things faster. You will be able to know which foot type gives you sprint if you hover mouse over it and look at what it can do. If you add the Sprint Pack accessory from the Captain Outfitter, Sprint will be replaced with Sprint Burst, which serves the same purpose, but requires energy to use. In the Test Drive you won't be able to see how fast your creature goes using Sprint as the creature only runs in place. Also, sprint helps while chasing down prey as well as running away from enemies. Using sprint with a jump of some sort will almost double the distance traveled through the air.
If you are trying to create a creature based on attack in the tribal stage, sprint becomes a very useful tool. For instance: If an opposing tribe manages to steal food from your food pile, sprint allows you to catch up and stop the thief. It also helps in the stealing process.