You can start training your dog before they're of age to compete. Begin by working on basic obedience and teach your puppy to sit, lie down, come, heel, and stay. Your puppy will also benefit from attending training classes where they will learn basic obedience and get used to working around lots of other dogs and people. Having your pet take and pass the AKC Good Citizen Test is a helpful step.
Tunnels: There are a couple of different types of tunnels used in agility competition. One type is a tube with a U-shaped bend that is made of joined rigid hoops. Another style consists of a stiff collar-like tunnel, usually only a few feet long, that has a length of fabric fastened to one end. The dog goes in through the collar portion and must find its way out from under the collapsed fabric portion.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.