In AKC Tracking, your dog uses his nose to find a pre-placed item within the working area. Tracking is one of the only sports in which you have to completely rely on your dog's skills: the dog is completely in charge. The dog is the expert because he knows how to use his nose to follow the track. The handler will learn to read the dog's body language to determine when the dog is on track, and when to encourage him to keep looking!
Tracking classes are offered by many dog clubs including the Wenatchee Kennel Club. There are also many excellent books that discuss and explaing training your dog to track.