Before you sign up, go out to visit the class one night, and just watch. When class is over, go up and ask questions if you've got any. If all the dogs in the class happen to be large breeds, it might be a good idea to ask the instructor if he or she has trained or worked with any small breeds of dogs. Agility training should be kept up beat and fun. You'll use food to teach your dogs the different obstacles, and food or toys or even both as rewards.
Hot dogs work well, too.
Or there are all sorts of soft commercial dog treats available, too. Find a couple different ones that your dog really thinks are special. Remember to make allowances at suppertime, though. There are several organizations that offer agility competition and titles. The AKC offers several agility titles, and is making plans to add more.