Basically, there's a maze constructed of hay bales, and within that maze are hidden rats, safely contained within PVC tubes. There are also PVC tubes that contain rat bedding without a live rat, and empty tubes. Number of each depends on the level (starts with one of each). The dog has to search and find the rats, the handler recognizes when the dog has found a rat, and calls the find. The dog is also required to go through a tunnel made of hay bales at some point during the course, and to climb onto one of the bales. If you find all the rats, without error, and do the climb and the tunnel, the dog qualifies.
Training is minimal, and depends somewhat on the dog. Many dogs don't need training at all. Finding the rat is instinctive behavior. Some dogs need to be introduced to the quarry to bring out their prey drive. Some dogs need a little training to do tunnels, and surprisingly to me, to climb on the bales. (mine love to jump on the bales). The harder part is usually for the handler to learn to read their dog's alert.